Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 5: Integrals - Section 5.6 - Definite Integral Substitutions and the Area Between Curves - Exercises 5.6 - Page 304: 39

Answer

$\displaystyle \frac{49}{6}$

Work Step by Step

The area between two graphs over [a,b], where one graph is above the other, is given with $\displaystyle \int_{a}^{b}(y_{above}-y_{below})dx$. --- For $x\in[-2,-1]$ and $x\in[2,3],\ \ $ $y_{above}=-x+2,\ \ y_{below}=4-x^{2}$ $A_{1}=\displaystyle \int_{-2}^{-1}[(-x+2)-(4-x^{2})]dx=\int_{-2}^{-1}[x^{2}-x-2]dx= \left[\frac{x^{3}}{3}-\frac{x^{2}}{2}-2x \right]_{-2}^{-1}$ $= \displaystyle \frac{-1+8}{3}-\frac{1-4}{2}-2(-1+2) =\frac{11}{6}$ $A_{3}=\displaystyle \int_{2}^{3}[(-x+2)-(4-x^{2})]dx=\int_{2}^{3}[x^{2}-x-2]dx= \left[\frac{x^{3}}{3}-\frac{x^{2}}{2}-2x \right]_{2}^{3}$ $= \displaystyle \left[ \frac{27-8}{3}-\frac{9-4}{2}-2(3-2) \right]=\frac{11}{6}$ In the middle interval, $x\in[-1,2],$ $y_{above}=4-x^{2},\ \ y_{below}= -x+2$ $A_{2}=\displaystyle \int_{-1}^{2}[(4-x^{2})-(-x+2)]dx=-\int_{-1}^{2}[x^{2}-x-2]dx= -\left[\frac{x^{3}}{3}-\frac{x^{2}}{2}-2x \right]_{-1}^{2}$ $=- \displaystyle \left[ \frac{8+1}{3}-\frac{2+1}{2}-2(2+1) \right]=\frac{9}{2}$ Total area = $A_{1}+A_{2}+A_{3}=\displaystyle \frac{11}{6}+ \frac{9}{2}+\frac{11}{6}=\frac{49}{6}$
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