Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter P - Review Exercises - Page 143: 122

Answer

The simplified value of the expression is $\frac{25\sqrt{\left( 25-{{x}^{2}} \right)}}{{{\left( 5-x \right)}^{2}}{{\left( 5+x \right)}^{2}}}$.

Work Step by Step

Consider the expression $\frac{\sqrt{25-{{x}^{2}}}+\frac{{{x}^{2}}}{\sqrt{25-{{x}^{2}}}}}{25-{{x}^{2}}}$. Here, the least common denominator is $\sqrt{25-{{x}^{2}}}$. So, multiply the numerator and denominator by $\sqrt{25-{{x}^{2}}}$ , That is, $\begin{align} & \frac{\sqrt{25-{{x}^{2}}}+\frac{{{x}^{2}}}{\sqrt{25-{{x}^{2}}}}}{25-{{x}^{2}}}\cdot \frac{\sqrt{25-{{x}^{2}}}}{\sqrt{25-{{x}^{2}}}}=\frac{\sqrt{25-{{x}^{2}}}\cdot \sqrt{25-{{x}^{2}}}+\frac{{{x}^{2}}}{\sqrt{25-{{x}^{2}}}}\cdot \sqrt{25-{{x}^{2}}}}{25-{{x}^{2}}\cdot \sqrt{25-{{x}^{2}}}} \\ & =\frac{25-{{x}^{2}}+{{x}^{2}}}{{{\left( 25-{{x}^{2}} \right)}^{1}}\cdot {{\left( 25-{{x}^{2}} \right)}^{\frac{1}{2}}}} \\ & =\frac{25}{{{\left( 25-{{x}^{2}} \right)}^{1+\frac{1}{2}}}} \\ & =\frac{25}{{{\left( 25-{{x}^{2}} \right)}^{\frac{3}{2}}}} \end{align}$ Further simplify the above expression: $\begin{align} & \frac{\sqrt{25-{{x}^{2}}}+\frac{{{x}^{2}}}{\sqrt{25-{{x}^{2}}}}}{25-{{x}^{2}}}\cdot \frac{\sqrt{25-{{x}^{2}}}}{\sqrt{25-{{x}^{2}}}}=\frac{25}{\sqrt{{{\left( 25-{{x}^{2}} \right)}^{3}}}} \\ & =\frac{25}{\sqrt{{{\left( 25-{{x}^{2}} \right)}^{3}}}}\cdot \frac{\sqrt{\left( 25-{{x}^{2}} \right)}}{\sqrt{\left( 25-{{x}^{2}} \right)}} \\ & =\frac{25\sqrt{\left( 25-{{x}^{2}} \right)}}{\left( 25-{{x}^{2}} \right)\left( 25-{{x}^{2}} \right)} \\ & =\frac{25\sqrt{\left( 25-{{x}^{2}} \right)}}{\left( {{5}^{2}}-{{x}^{2}} \right)\left( {{5}^{2}}-{{x}^{2}} \right)} \end{align}$ Apply the difference of the square property in the denominator as shown: $\begin{align} & \frac{\sqrt{25-{{x}^{2}}}+\frac{{{x}^{2}}}{\sqrt{25-{{x}^{2}}}}}{25-{{x}^{2}}}\cdot \frac{\sqrt{25-{{x}^{2}}}}{\sqrt{25-{{x}^{2}}}}=\frac{25\sqrt{\left( 25-{{x}^{2}} \right)}}{\left( {{5}^{2}}-{{x}^{2}} \right)\left( {{5}^{2}}-{{x}^{2}} \right)} \\ & =\frac{25\sqrt{\left( 25-{{x}^{2}} \right)}}{\left( 5-x \right)\left( 5+x \right)\left( 5-x \right)\left( 5+x \right)} \\ & =\frac{25\sqrt{\left( 25-{{x}^{2}} \right)}}{{{\left( 5-x \right)}^{2}}{{\left( 5+x \right)}^{2}}} \end{align}$ Hence, the simplified value of the expression is $\frac{25\sqrt{\left( 25-{{x}^{2}} \right)}}{{{\left( 5-x \right)}^{2}}{{\left( 5+x \right)}^{2}}}$.
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