Big Ideas Math - Algebra 1, A Common Core Curriculum

Published by Big Ideas Learning LLC
ISBN 10: 978-1-60840-838-2
ISBN 13: 978-1-60840-838-2

Chapter 6 - Exponential Functions and Sequences - Maintaining Mathematical Proficiency - Page 289: 11

Answer

The product of perfect squares is always a perfect square The quotient of perfect squares is not always a perfect square

Work Step by Step

Let $a^{2}$ and $b^{2}$ be the squares of integers $a$ and $b$. The product of the squares equals $$a^{2}b^{2}=(a\cdot a)(b\cdot b) $$ Since multiplication is associative, we can select any two neighboring factors to be multiplied first $$ a^{2}b^{2}=a\cdot(ab)\cdot b $$ Since multiplication is commutative, the first two factors can change places: $$\begin{align*} a^{2}b^{2}&=(ab)\cdot a\cdot b & & \\ & =(ab)(ab) \\ & =(ab)^{2} \end{align*}$$ so the product of perfect squares is a perfect square, because $ab$ is a product of integers (an integer.) Now, let $a=5$ and $b=2$. The quotient of $a^{2}=25$ and $b^{2}=4$ is $$ \frac{a^{2}}{b^{2}}=\frac{25}{4},$$ which is not an integer.
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