Chapter 1: Problem 13
Pythagorean Triples. Three natural numbers \(a, b,\) and \(c\) with \(a
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Chapter 1: Problem 13
Pythagorean Triples. Three natural numbers \(a, b,\) and \(c\) with \(a
These are the key concepts you need to understand to accurately answer the question.
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More Work with Pythagorean Triples. In Exercise (13), we verified that each of the following triples of natural numbers are Pythagorean triples: $$ \begin{array}{lll} \cdot 3,4, \text { and } 5 & \bullet 8,15, \text { and } 17 & \bullet 12,35, \text { and } 37 \\ \cdot 6,8, \text { and } 10 & \bullet 10,24, \text { and } 26 & \bullet 14,48, \text { and } 50 \end{array} $$ (a) Focus on the least even natural number in each of these Pythagorean triples. Let \(n\) be this even number and find \(m\) so that \(n=2 m .\) Now try to write formulas for the other two numbers in the Pythagorean triple in terms of \(m\). For example, for \(3,4,\) and \(5, n=4\) and \(m=2,\) and for 8\. \(15,\) and \(17, n=8\) and \(m=4 .\) Once you think you have formulas. test your results with \(m=10\). That is, check to see that you have a Pythagorean triple whose smallest even number is 20 . (b) Write a proposition and then write a proof of the proposition. The proposition should be in the form: If \(m\) is a natural number and \(m \geq 2\), then \(\ldots \ldots\)
Exploring Propositions. In Progress Check 1.2, we used exploration to show that certain statements were false and to make conjectures that certain statements were true. We can also use exploration to formulate a conjecture that we believe to be true. For example, if we calculate successive powers of \(2\left(2^{1}, 2^{2}, 2^{3}, 2^{4}, 2^{5}, \ldots\right)\) and examine the units digits of these numbers, we could make the following conjectures (among others): \- If \(n\) is a natural number, then the units digit of \(2^{n}\) must be \(2,4,6,\) or 8 . \- The units digits of the successive powers of 2 repeat according to the pattern " 2,4,8,6 ." (a) Is it possible to formulate a conjecture about the units digits of successive powers of \(4\left(4^{1}, 4^{2}, 4^{3}, 4^{4}, 4^{5}, \ldots\right) ?\) If so, formulate at least one conjecture. (b) Is it possible to formulate a conjecture about the units digit of numbers of the form \(7^{n}-2^{n},\) where \(n\) is a natural number? If so, formulate a conjecture in the form of a conditional statement in the form "If \(n\) is a natural number, then \(\ldots . "\) (c) Let \(f(x)=e^{2 x}\). Determine the first eight derivatives of this function. What do you observe? Formulate a conjecture that appears to be true. The conjecture should be written as a conditional statement in the form, "If \(n\) is a natural number, then \(\ldots . "\)
Following is a statement of a theorem which can be proven using the quadratic formula. For this theorem, \(a, b,\) and \(c\) are real numbers. Theorem If \(f\) is a quadratic function of the form \(f(x)=a x^{2}+b x+c\) and \(a c<0,\) then the function \(f\) has two \(x\) -intercepts. Using only this theorem, what can be concluded about the functions given by the following formulas? (a) \(g(x)=-8 x^{2}+5 x-2\) (b) \(h(x)=-\frac{1}{3} x^{2}+3 x\) (c) \(k(x)=8 x^{2}-5 x-7\) (d) \(j(x)=-\frac{71}{99} x^{2}+210\) (e) \(f(x)=-4 x^{2}-3 x+7\) (f) \(F(x)=-x^{4}+x^{3}+9\)
Construct a know-show table for each of the following statements and then write a formal proof for one of the statements. (a) If \(x\) is an even integer and \(y\) is an even integer, then \(x+y\) is an even integer. (b) If \(x\) is an even integer and \(y\) is an odd integer, then \(x+y\) is an odd integer. (c) If \(x\) is an odd integer and \(y\) is an odd integer, then \(x+y\) is an even integer.
Determine whether each of the following conditional statements is true or false. (a) If \(10<7,\) then \(3=4\). (c) If \(10<7,\) then \(3+5=8\). (b) If \(7<10,\) then \(3=4\). (d) If \(7<10,\) then \(3+5=8\).
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