Intermediate Algebra (12th Edition)

Published by Pearson
ISBN 10: 0321969359
ISBN 13: 978-0-32196-935-4

Chapter 7 - Section 7.6 - Solving Equations with Radicals - 7.6 Exercises - Page 485: 64


$A=\pi r^2$

Work Step by Step

$\bf{\text{Solution Outline:}}$ To solve the given formula, $ r=\sqrt{\dfrac{A}{\pi}} $ for $ A ,$ square both sides and then use cross-multiplication to isolate the needed variable. $\bf{\text{Solution Details:}}$ Squaring both sides of the given formula results to \begin{array}{l}\require{cancel} (r)^2=\left( \sqrt{\dfrac{A}{\pi}} \right)^2 \\\\ r^2=\dfrac{A}{\pi} .\end{array} Since $\dfrac{a}{b}=\dfrac{c}{d}$ implies $ad=bc$ or sometimes referred to as cross-multiplication, the equation above is equivalent to \begin{array}{l}\require{cancel} r^2(\pi)=1(A) \\\\ \pi r^2=A \\\\ A=\pi r^2 .\end{array}
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