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Prove that there are infinitely many solutions in positive integers \(x, y,\) and \(z\) to the equation \(x^{2}+y^{2}=\) \(z^{2} .\left[\text { Hint: Let } x=m^{2}-n^{2}, y=2 m n, \text { and } z=m^{2}+n^{2}\right.\) where \(m\) and \(n\) are integers. \(]\)

Short Answer

Expert verified
There are infinitely many solutions for x^2 + y^2 = z^2 using Pythagorean triples. Substituting x = m^2 - n^2, y = 2mn, and z = m^2 + n^2 proves this.

Step by step solution

01

- Understanding the Pythagorean Triple

The equation given is a form of the Pythagorean theorem: x^2 + y^2 = z^2 . These are known as Pythagorean triples.
02

- Substituting Variables

Substitute the given forms: x = m^2 - n^2, y = 2mn, z = m^2 + n^2 into the Pythagorean theorem equation.
03

- Simplifying the Equation

Plug in the substitutions: (m^2 - n^2)^2 + (2mn)^2 = (m^2 + n^2)^2 Expand and simplify the terms: (m^2 - n^2)^2 = (m^2 - n^2)(m^2 - n^2) = m^4 - 2m^2n^2 + n^4, (2mn)^2 = 4m^2n^2, (m^2 + n^2)^2 = (m^2 + n^2)(m^2 + n^2) = m^4 + 2m^2n^2 + n^4.
04

- Combining Like Terms

Combine like terms: m^4 - 2m^2n^2 + n^4 + 4m^2n^2 = m^4 + 2m^2n^2 + n^4 Results in: m^4 + 2m^2n^2 + n^4 = m^4 + 2m^2n^2 + n^4, which is a true statement.
05

- Conclusion

Since the equation holds true for any integers m and n, there are infinitely many pairs of positive integers x, y, and z that satisfy x^2 + y^2 = z^2. Hence, the equation has infinitely many positive integer solutions.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Pythagorean Triples
The Pythagorean theorem states that for any right-angled triangle, the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides. Mathematically, this is written as:
x^2 + y^2 = z^2
A Pythagorean triple is a set of three positive integers, (x, y, z), that satisfy this equation. Examples include (3, 4, 5) and (5, 12, 13). These sets are solutions to the Pythagorean theorem, where each number represents a side length of a right-angled triangle.
In our exercise, m and n are integers, and using the hint, you can generate Pythagorean triples by the formulas:
  • x = m^2 - n^2
  • y = 2mn
  • z = m^2 + n^2
This method guarantees that (x, y, z) will always satisfy the Pythagorean theorem.
Diophantine Equations
Diophantine equations are polynomial equations where we seek integer solutions. The equation is named after the ancient Greek mathematician Diophantus. These equations can take various forms, but they always require integer solutions.

One example is the linear equation of the form:
ax + by = c
where a, b, and c are given integers, and we are looking for integer values of x and y.

Our Pythagorean equation, x^2 + y^2 = z^2, is a classic example of a Diophantine equation. By solving it with integer solutions, we demonstrate that the solutions can be used for real-world applications, such as finding lengths in geometry.
Integer Solutions
When solving equations, finding integer solutions means we are only interested in whole numbers (positive or negative, including zero). These solutions are crucial in various fields of mathematics and practical applications, from computing to engineering.

In our exercise, we show that there are infinitely many integer solutions to the equation x^2 + y^2 = z^2. The formulas
  • x = m^2 - n^2
  • y = 2mn
  • z = m^2 + n^2
ensure that x, y, and z are integers for any integer values of m and n.
This concept has broad implications, as it shows the power of using simple algebraic manipulations to find integer solutions for more complex equations.
Mathematical Proofs
A mathematical proof is a logical argument demonstrating the truth of a mathematical statement. Proofs use previously established facts, such as theorems, axioms, and propositions. They are essential for validating mathematical concepts and ensuring their correctness.

Let's look at our exercise as a proof that there are infinitely many solutions in positive integers to the equation x^2 + y^2 = z^2. We used the hint, which involves specific substitutions:
  • x = m^2 - n^2
  • y = 2mn
  • z = m^2 + n^2
By substituting these into the Pythagorean theorem and simplifying, we verified that the equation holds true. This logical sequence of steps proves our statement.

Mathematical proofs are essential for understanding and verifying concepts in mathematics. They help build a foundation of knowledge that is reliable and logical.

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Most popular questions from this chapter

Use a proof by cases to show that 100 is not the cube of a positive integer. [Hint: Consider two cases: (i) \(1 \leq x \leq 4\) , (ii) \(x \geq 5 . ]\)

Use quantifiers and predicates with more than one variable to express these statements. a) Every computer science student needs a course in discrete mathematics. b) There is a student in this class who owns a personal computer. c) Every student in this class has taken at least one computer science course. d) There is a student in this class who has taken at least one course in computer science. e) Every student in this class has been in every building on campus. f ) There is a student in this class who has been in every room of at least one building on campus. g) Every student in this class has been in at least one room of every building on campus.

Prove that at least one of the real numbers \(a_{1}, a_{2}, \ldots, a_{n}\) is greater than or equal to the average of these numbers. What kind of proof did you use?

Express each of these statements using mathematical and logical operators, predicates, and quantifiers, where the domain consists of all integers. a) The sum of two negative integers is negative. b) The difference of two positive integers is not necessarily positive. c) The sum of the squares of two integers is greater than or equal to the square of their sum. d) The absolute value of the product of two integers is the product of their absolute values.

Show that the product of two of the numbers \(65^{1000}-\) \(8^{2001}+3^{177}, 79^{1212}-9^{2399}+2^{2001},\) and \(24^{493}-5^{8192}+\) \(7^{1777}\) is nonnegative. Is your proof constructive or non-constructive? [Hint: Do not try to evaluate these numbers!]

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