Solve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more. Symbolab is the best step by step calculator for a wide range of math problems, from basic arithmetic to advanced calculus and linear algebra. It shows you the solution, graph, detailed steps and explanations for each problem. Free math problem solver answers your algebra, geometry, trigonometry, calculus, and statistics homework questions with step-by-step explanations, just like a math tutor.Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.For Question 1, observe that Z = (B×X)∩V. (Just notice that x ∈ V b means (b,x)∈ V .) Question 2: consider the map f:(B×C)×Pn → (B ×Pn)×(C ×Pn), (b,c,x) ↦((b,x),(c,x)). ... The problem is that in order to remedy the problems and paradoxes of naive set theory, the mathematicians around the turn of the century realised that you ... Free math lessons and math homework help from basic math to algebra, geometry and beyond. Students, teachers, parents, and everyone can find solutions to their math problems instantly., the numerator is 3, and the denominator is 8. A more illustrative example could involve a pie with 8 slices. 1 of those 8 slices would constitute the numerator of a fraction, while the total of 8 slices that comprises the whole pie would be the denominator. If a person were to eat 3 slices, the remaining fraction of the pie would therefore beB- 8. Which expression is equivalent to (StartFraction 125 squared Over 125 Superscript four-thirds Baseline EndFraction? D- 25. Which of the following is equivalent to 36 Superscript negative one-half? D- 1/6. Which expression is equivalent to (x Superscript 27 Baseline y) Superscript one-third? B- x^9 (3cubed squareroot y)By ‘ The law of exponents ‘ , a^n × a^m = a^n+m. Therefore , e^x × e^x = e^x+x = e^2x . Find out how many invertible and diagonal solutions X 2 − 2X = 0 has when X ∈ R3×3. If X is invertible, then multiplying each side of X 2−2X = 0 by the inverse of X gives us that X −2I = 0 and so X = 2I. For the case where X is diagonal, let X ... , the numerator is 3, and the denominator is 8. A more illustrative example could involve a pie with 8 slices. 1 of those 8 slices would constitute the numerator of a fraction, while the total of 8 slices that comprises the whole pie would be the denominator. If a person were to eat 3 slices, the remaining fraction of the pie would therefore be The fraction calculator is easy to use. First select if you want to use the default or mixed fraction calculator. Fill in two fractions and choose if you want to add, subtract, multiply or divide and click the "Calculate" button. The result is a (mixed) fraction reduced to it’s simplest form. Also a table with the result fraction converted in ...Free Algebraic Properties Calculator - Simplify radicals, exponents, logarithms, absolute values and complex numbers step-by-step , the numerator is 3, and the denominator is 8. A more illustrative example could involve a pie with 8 slices. 1 of those 8 slices would constitute the numerator of a fraction, while the total of 8 slices that comprises the whole pie would be the denominator. If a person were to eat 3 slices, the remaining fraction of the pie would therefore beCalculus. Solve for x 1/x=0. 1 x = 0 1 x = 0. Set the numerator equal to zero. 1 = 0 1 = 0. Since 1 ≠ 0 1 ≠ 0, there are no solutions.To write 1 y 1 y as a fraction with a common denominator, multiply by x x x x. 1 x ⋅ y y + 1 y ⋅ x x 1 x ⋅ y y + 1 y ⋅ x x. Write each expression with a common denominator of xy x y, by multiplying each by an appropriate factor of 1 1. Tap for more steps... y xy + x xy y x y + x x y. Combine the numerators over the common denominator.The pH scale is logarithmic, meaning that an increase or decrease of an integer value changes the concentration by a tenfold. For example, a pH of 3 is ten times more acidic than a pH of 4. Likewise, a pH of 3 is one hundred times more acidic than a pH of 5. Similarly a pH of 11 is ten times more basic than a pH of 10.Add, subtract, multiply and divide decimal numbers with this calculator. You can use: Positive or negative decimals. For negative numbers insert a leading negative or minus sign before your number, like this: -45 or -356.5. Integers, decimals or scientific notation. For scientific notation use "e" notation like this: -3.5e8 or 4.7E-9.An exponent is a way to represent how many times a number, known as the base, is multiplied by itself. It is represented as a small number in the upper right hand corner of the base. For example: x² means you multiply x by itself two times, which is x × x. Likewise, 4² = 4 × 4, etc. If the exponent is 3, in the example 5³, then the result ...May 25, 2020 · Which expression is equivalent to log Subscript 12 Baseline StartFraction x Superscript 4 Baseline StartRoot x cubed minus 2 EndRoot Over (x + 1) Superscript 5 Baseline EndFraction? 4 log Subscript 12 Baseline x + one-half log Subscript 12 Baseline (x cubed minus 2) minus 5 log Subscript 12 Baseline (x times 1) Sounds tough, but once you have mastered the 10× table, it is just a few steps away. Firstly, 11× is mostly easy: from 11×2 to 11×9 you just put the two digits together. 11×2=22, 11×3=33, ..., 11×9=99. And of course 2×, 5× and 10× just follow their simple rules you know already. So it just leaves these to remember:You enter the first fraction, you enter the second fraction, click "Calculate" and hey presto, you get the answer. You can also click the little icon after the calculator to find out more information about the process of subtracting one fraction from another. (Note: you need to have performed a calculation first or the link won't work!) Symbolab is the best step by step calculator for a wide range of math problems, from basic arithmetic to advanced calculus and linear algebra. It shows you the solution, graph, detailed steps and explanations for each problem.Algebra. Multiply (x-5) (x-1) (x − 5) (x − 1) ( x - 5) ( x - 1) Expand (x−5)(x− 1) ( x - 5) ( x - 1) using the FOIL Method. Tap for more steps... x⋅x+x⋅ −1−5x−5⋅−1 x ⋅ x + x ⋅ - 1 - 5 x - 5 ⋅ - 1. Simplify and combine like terms. Tap for more steps... x2 − 6x+5 x 2 - 6 x + 5.Solve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more.Long Multiplication Example: Multiply 234 by 56. Long Multiplication Steps: Stack the numbers with the larger number on top. Align the numbers by place value columns. Multiply the ones digit in the bottom number by each digit in the top number. 6 × 4 = 24. Put the 4 in Ones place. Carry the 2 to Tens place.In algebra, a quadratic equation is any equation that can be rearranged in standard form as where x represents an unknown value, and a, b, and c represent known numbers, where a ≠ 0. An exponent is a way to represent how many times a number, known as the base, is multiplied by itself. It is represented as a small number in the upper right hand corner of the base. For example: x² means you multiply x by itself two times, which is x × x. Likewise, 4² = 4 × 4, etc. If the exponent is 3, in the example 5³, then the result ...Long Multiplication Example: Multiply 234 by 56. Long Multiplication Steps: Stack the numbers with the larger number on top. Align the numbers by place value columns. Multiply the ones digit in the bottom number by each digit in the top number. 6 × 4 = 24. Put the 4 in Ones place. Carry the 2 to Tens place.In algebra, a quadratic equation is any equation that can be rearranged in standard form as where x represents an unknown value, and a, b, and c represent known numbers, where a ≠ 0. Compute answers using Wolfram's breakthrough technology & knowledgebase, relied on by millions of students & professionals. For math, science, nutrition, history ...Solve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more. That you could view as x to the negative 1. You have a first power here. 1 minus 2 is negative 1. So this right here is equal to x to the negative 1 power. Or it could also be equal to 1 over x. These are equivalent. So let's say that this is equal into 1 over x, just like that. And it would be. x over x times x.X-Times is a technology company that creates high-end digital chip design solutions. The company is focusing on independent research and development of the digital implementation EDA platform in accordance with the 3S concept (Smart, Speedy, Simple), including a new generation of layout and wiring technology while providing high-end digital chipThe fraction calculator is easy to use. First select if you want to use the default or mixed fraction calculator. Fill in two fractions and choose if you want to add, subtract, multiply or divide and click the "Calculate" button. The result is a (mixed) fraction reduced to it’s simplest form. Also a table with the result fraction converted in ... Defintion of proper homotopy https://math.stackexchange.com/questions/2532344/defintion-of-proper-homotopy Let X =R. The homotopy will be from the identity map to itself, so H (0,x)= H (1,x)= x for all x. For each integer n ≥ 1, during the time period [1/(n+1),1/n], the point n∈ X is ...Just like for the matrix-vector product, the product AB A B between matrices A A and B B is defined only if the number of columns in A A equals the number of rows in B B. In math terms, we say we can multiply an m × n m × n matrix A A by an n × p n × p matrix B B. (If p p happened to be 1, then B B would be an n × 1 n × 1 column vector ... Simplify 1/ ( square root of x) 1 √x 1 x. Multiply 1 √x 1 x by √x √x x x. 1 √x ⋅ √x √x 1 x ⋅ x x. Combine and simplify the denominator. In algebra, a quadratic equation is any equation that can be rearranged in standard form as where x represents an unknown value, and a, b, and c represent known numbers, where a ≠ 0.Multiply the inside terms: 1 ⋅ x = x. Multiply the last term: 1 ⋅ − 1 = − 1. This is equal to. x2 +x −x −1. The middle terms cancel, and we're left with. x2 −1. Remember, FOIL will work every time, but if we see a product of binomials of the form (a + b)(a −b), we can immediately recognize that it fits the difference of squares ...First we prove an intermediate result. Subtract 0 × 0 0 × 0 from each side to get 0 = 0 × 0 0 = 0 × 0. Now we are ready for the final kill. = 1 × 1 + 1 × (−1) + (−1) × 1 + (−1) × (−1) = 1 × 1 + 1 × ( − 1) + ( − 1) × 1 + ( − 1) × ( − 1) Add 1 1 to each side to get 1 = (−1) × (−1) 1 = ( − 1) × ( − 1). 25.6k 4 ...Simplify x^ (1/2)*x^ (1/2) x1 2 ⋅ x1 2 x 1 2 ⋅ x 1 2. Multiply x1 2 x 1 2 by x1 2 x 1 2 by adding the exponents. Tap for more steps... x1 x 1. Simplify x1 x 1.Step 1: Enter the radical expression below for which you want to calculate the square root. The square root calculator finds the square root of the given radical expression. If a given number is a perfect square, you will get a final answer in exact form. If a given number is not a perfect square, you will get a final answer in exact form and ... First we prove an intermediate result. Subtract 0 × 0 0 × 0 from each side to get 0 = 0 × 0 0 = 0 × 0. Now we are ready for the final kill. = 1 × 1 + 1 × (−1) + (−1) × 1 + (−1) × (−1) = 1 × 1 + 1 × ( − 1) + ( − 1) × 1 + ( − 1) × ( − 1) Add 1 1 to each side to get 1 = (−1) × (−1) 1 = ( − 1) × ( − 1). 25.6k 4 ... By ‘ The law of exponents ‘ , a^n × a^m = a^n+m. Therefore , e^x × e^x = e^x+x = e^2x . Find out how many invertible and diagonal solutions X 2 − 2X = 0 has when X ∈ R3×3. If X is invertible, then multiplying each side of X 2−2X = 0 by the inverse of X gives us that X −2I = 0 and so X = 2I. For the case where X is diagonal, let X ... , the numerator is 3, and the denominator is 8. A more illustrative example could involve a pie with 8 slices. 1 of those 8 slices would constitute the numerator of a fraction, while the total of 8 slices that comprises the whole pie would be the denominator. If a person were to eat 3 slices, the remaining fraction of the pie would therefore bex squared is a notation that is used to represent the expression \(x\times x\). i.e., x squared equals x multiplied by itself.Just like for the matrix-vector product, the product AB A B between matrices A A and B B is defined only if the number of columns in A A equals the number of rows in B B. In math terms, we say we can multiply an m × n m × n matrix A A by an n × p n × p matrix B B. (If p p happened to be 1, then B B would be an n × 1 n × 1 column vector ... Apr 29, 2023 · An exponent is a way to represent how many times a number, known as the base, is multiplied by itself. It is represented as a small number in the upper right hand corner of the base. For example: x² means you multiply x by itself two times, which is x × x. Likewise, 4² = 4 × 4, etc. If the exponent is 3, in the example 5³, then the result ... How to Use the Calculator. Type your algebra problem into the text box. For example, enter 3x+2=14 into the text box to get a step-by-step explanation of how to solve 3x+2=14. Simplify x^ (1/2)*x^ (1/2) x1 2 ⋅ x1 2 x 1 2 ⋅ x 1 2. Multiply x1 2 x 1 2 by x1 2 x 1 2 by adding the exponents. Tap for more steps... x1 x 1. Simplify x1 x 1. Sep 2, 2012 · The numpy.repeat has been mentioned, and that's clearly the equivalent to what you want. But for completenes' sake, there's also repeat from the itertools standard library. . However, this is intended for iterables in general, so it doesn't allow repetions by index (because iterables in general do not have an index defin Associative property of multiplication: Changing the grouping of factors does not change the product. For example, (2 \times 3) \times 4 = 2 \times (3 \times 4) (2×3)×4 = 2×(3×4). Identity property of multiplication: The product of 1 1 and any number is that number. For example, 7 \times 1 = 7 7 ×1 = 7. Associative property of multiplication: Changing the grouping of factors does not change the product. For example, (2 \times 3) \times 4 = 2 \times (3 \times 4) (2×3)×4 = 2×(3×4). Identity property of multiplication: The product of 1 1 and any number is that number. For example, 7 \times 1 = 7 7 ×1 = 7.Dec 18, 2022 · (x) x 1 =x. Why is a number to the first power equal the same number? The following is not a proof or a reason, but it's a demonstrationthat might be intuitively satisfying:'X' mentioned 4 times: X times X times X times X = X to the fourth power'X' mentioned 3 times: X times X times X = X to the third power'X' mentioned 2 times: X times X = X to the second power'X' mentioned 1 time: X = X to ... Suppose that Am×nx = 0 has a nontrivial solution x. Prove that, for some row vector z, the equation yA = z has no solution. Assume for contradiction that yA =z has a solution y for all vectors z. Now, multiply on the right by x. This gives, yAx= zx⇒ y(0)= zx⇒ zx = 0. Then, since x is not the zero ...The fraction calculator is easy to use. First select if you want to use the default or mixed fraction calculator. Fill in two fractions and choose if you want to add, subtract, multiply or divide and click the "Calculate" button. The result is a (mixed) fraction reduced to it’s simplest form. Also a table with the result fraction converted in ...For X\times [0,M]: \times is the Cartesian product and [0,M] is the interval \{x:0 \le x \le M\}. So, X \times [0,M] = \{(x,r):x \in X \land 0 \le r \le M\} For Y ...In algebra, a quadratic equation is any equation that can be rearranged in standard form as where x represents an unknown value, and a, b, and c represent known numbers, where a ≠ 0. See the entire simplification process below: Explanation: The rules for order of operation say to execute the multiplication in this problem first: 2x−9×x+8 →2x−9x+8 ... Equivalent metrics gives the same topology, so we can show that the metrics are equivalent, I'll replace d(x1,y1)= x and d(x2,y2) = y and show that they are equivalent.You enter the first fraction, you enter the second fraction, click "Calculate" and hey presto, you get the answer. You can also click the little icon after the calculator to find out more information about the process of subtracting one fraction from another. (Note: you need to have performed a calculation first or the link won't work!) Solve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more.Free math problem solver answers your algebra, geometry, trigonometry, calculus, and statistics homework questions with step-by-step explanations, just like a math tutor.Like, what does “multiply ‘x’ by itself -1 times” mean? The expression x n only means “multiply x by itself n times” when n is a positive integer. When the exponent is 0, a negative integer, an arbitrary rational number, an arbitrary real number, or an arbitrary complex number you need a different definition for x n to make sense ...Identify H (A) and H (B) with H (pt). Then f ∗ = (g∗,−g∗), so kerf ∗ = kerg∗. Proof that Sorgenfrey plane is not normal using points x × (-x) They mean all x,−x +ϵ such that x ∈ (a,b) and 0 < ϵ < 1/n; that includes both rational and irrational x. You have a particular n and a non-empty open interval (a,b) ...All the constructions that you used to define the isomorphism are natural/functorial: Given a map X →Y, you have a natural map that respect inclusions, which gives a starting point for all the ... Let X =R. The homotopy will be from the identity map to itself, so H (0,x)= H (1,x)= x for all x. For each integer n ≥ 1, during the time period ... Free Algebraic Properties Calculator - Simplify radicals, exponents, logarithms, absolute values and complex numbers step-by-step To add or subtract expressions, expand them to make their denominators the same. Least common multiple of x-1 and x+1 is \left(x-1\right)\left(x+1\right).Get the free "Solve for X Calculator" widget for your website, blog, Wordpress, Blogger, or iGoogle. Find more Mathematics widgets in Wolfram|Alpha.In order to show that T is a function, you need to prove that for each pair of subsets A and B of X there is one and only one subset U of X\times X such that T(A,B)=U, that is, ((A,B),U) \in T ... What is the ''right" norm for the Banach space tensor product in this situation?Simplify ( square root of x-1)( square root of x+1) Step 1. Expand using the FOIL Method. Tap for more steps... Step 1.1. Apply the distributive property. Step 1.2.Add, subtract, multiply and divide decimal numbers with this calculator. You can use: Positive or negative decimals. For negative numbers insert a leading negative or minus sign before your number, like this: -45 or -356.5. Integers, decimals or scientific notation. For scientific notation use "e" notation like this: -3.5e8 or 4.7E-9.In algebra, a quadratic equation is any equation that can be rearranged in standard form as where x represents an unknown value, and a, b, and c represent known numbers, where a ≠ 0.Associative property of multiplication: Changing the grouping of factors does not change the product. For example, (2 \times 3) \times 4 = 2 \times (3 \times 4) (2×3)×4 = 2×(3×4). Identity property of multiplication: The product of 1 1 and any number is that number. For example, 7 \times 1 = 7 7 ×1 = 7.Compute answers using Wolfram's breakthrough technology & knowledgebase, relied on by millions of students & professionals. For math, science, nutrition, history ...Nov 12, 2018 · Add, subtract, multiply and divide decimal numbers with this calculator. You can use: Positive or negative decimals. For negative numbers insert a leading negative or minus sign before your number, like this: -45 or -356.5. Integers, decimals or scientific notation. For scientific notation use "e" notation like this: -3.5e8 or 4.7E-9. , the numerator is 3, and the denominator is 8. A more illustrative example could involve a pie with 8 slices. 1 of those 8 slices would constitute the numerator of a fraction, while the total of 8 slices that comprises the whole pie would be the denominator. If a person were to eat 3 slices, the remaining fraction of the pie would therefore beSee the entire simplification process below: Explanation: The rules for order of operation say to execute the multiplication in this problem first: 2x−9×x+8 →2x−9x+8 ... Equivalent metrics gives the same topology, so we can show that the metrics are equivalent, I'll replace d(x1,y1)= x and d(x2,y2) = y and show that they are equivalent.You want to have your decimal q such that q \times (1.15 \times x ) = 1.15 \times x - x = 0.15 \times x so q \times 1.15 \times x = 0.15 \times x for all x Finally, you have q = \frac{0.15}{1.15} \simeq 0.1304347826 ...X-Times is a technology company that creates high-end digital chip design solutions. The company is focusing on independent research and development of the digital implementation EDA platform in accordance with the 3S concept (Smart, Speedy, Simple), including a new generation of layout and wiring technology while providing high-end digital chipSolve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more. Solve your math problems using our free math solver with step-by-step solutions. Our math solver supports basic math, pre-algebra, algebra, trigonometry, calculus and more.Associative property of multiplication: Changing the grouping of factors does not change the product. For example, (2 \times 3) \times 4 = 2 \times (3 \times 4) (2×3)×4 = 2×(3×4). Identity property of multiplication: The product of 1 1 and any number is that number. For example, 7 \times 1 = 7 7 ×1 = 7. B- 8. Which expression is equivalent to (StartFraction 125 squared Over 125 Superscript four-thirds Baseline EndFraction? D- 25. Which of the following is equivalent to 36 Superscript negative one-half? D- 1/6. Which expression is equivalent to (x Superscript 27 Baseline y) Superscript one-third? B- x^9 (3cubed squareroot y)You want to have your decimal q such that q \times (1.15 \times x ) = 1.15 \times x - x = 0.15 \times x so q \times 1.15 \times x = 0.15 \times x for all x Finally, you have q = \frac{0.15}{1.15} \simeq 0.1304347826 ...Solve for x sin (x)=1. sin(x) = 1 sin ( x) = 1. Take the inverse sine of both sides of the equation to extract x x from inside the sine. x = arcsin(1) x = arcsin ( 1) Simplify the right side. Tap for more steps... x = π 2 x = π 2. The sine function is positive in the first and second quadrants. To find the second solution, subtract the ...
For X\times [0,M]: \times is the Cartesian product and [0,M] is the interval \{x:0 \le x \le M\}. So, X \times [0,M] = \{(x,r):x \in X \land 0 \le r \le M\} For Y .... Referenzen
Online math solver with free step by step solutions to algebra, calculus, and other math problems. Get help on the web or with our math app. (x) x 1 =x. Why is a number to the first power equal the same number? The following is not a proof or a reason, but it's a demonstrationthat might be intuitively satisfying:'X' mentioned 4 times: X times X times X times X = X to the fourth power'X' mentioned 3 times: X times X times X = X to the third power'X' mentioned 2 times: X times X = X to the second power'X' mentioned 1 time: X = X to ...For Question 1, observe that Z = (B×X)∩V. (Just notice that x ∈ V b means (b,x)∈ V .) Question 2: consider the map f:(B×C)×Pn → (B ×Pn)×(C ×Pn), (b,c,x) ↦((b,x),(c,x)). ... The problem is that in order to remedy the problems and paradoxes of naive set theory, the mathematicians around the turn of the century realised that you ... Find the values of a and b that make the second expression equivalent to the first expression. Assume that x > 0 and y ≥ 0. StartRoot StartFraction 126 x y Superscript 5 Baseline Over 32 x cubed EndFraction EndRoot = StartRoot StartFraction 63 y Superscript 5 Baseline Over a x Superscript b Baseline EndFraction EndRoot a = and b =Sounds tough, but once you have mastered the 10× table, it is just a few steps away. Firstly, 11× is mostly easy: from 11×2 to 11×9 you just put the two digits together. 11×2=22, 11×3=33, ..., 11×9=99. And of course 2×, 5× and 10× just follow their simple rules you know already. So it just leaves these to remember:Just like for the matrix-vector product, the product AB A B between matrices A A and B B is defined only if the number of columns in A A equals the number of rows in B B. In math terms, we say we can multiply an m × n m × n matrix A A by an n × p n × p matrix B B. (If p p happened to be 1, then B B would be an n × 1 n × 1 column vector ... Solved X Times Examples: 12x X 2x = ? 12x X 2x = 24x 2. 4x X 2x = ? 4x X 2x =8 2. 2x X 6x = ? 2x X 6x = 12x 2. 3x X 3x = ? 3x X 3x = 9x 2. 9x X 27x = ? 9x X 27x = 243 ...Online math solver with free step by step solutions to algebra, calculus, and other math problems. Get help on the web or with our math app. Free math problem solver answers your algebra, geometry, trigonometry, calculus, and statistics homework questions with step-by-step explanations, just like a math tutor.The fraction calculator is easy to use. First select if you want to use the default or mixed fraction calculator. Fill in two fractions and choose if you want to add, subtract, multiply or divide and click the "Calculate" button. The result is a (mixed) fraction reduced to it’s simplest form. Also a table with the result fraction converted in ...Free Algebraic Properties Calculator - Simplify radicals, exponents, logarithms, absolute values and complex numbers step-by-stepDefintion of proper homotopy https://math.stackexchange.com/questions/2532344/defintion-of-proper-homotopy Let X =R. The homotopy will be from the identity map to itself, so H (0,x)= H (1,x)= x for all x. For each integer n ≥ 1, during the time period [1/(n+1),1/n], the point n∈ X is ...How to Use the Calculator. Type your algebra problem into the text box. For example, enter 3x+2=14 into the text box to get a step-by-step explanation of how to solve 3x+2=14.Identify H (A) and H (B) with H (pt). Then f ∗ = (g∗,−g∗), so kerf ∗ = kerg∗. Proof that Sorgenfrey plane is not normal using points x × (-x) They mean all x,−x +ϵ such that x ∈ (a,b) and 0 < ϵ < 1/n; that includes both rational and irrational x. You have a particular n and a non-empty open interval (a,b) ....