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: 37

Answer

$\displaystyle \frac{38}{3}$

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 $x\in[-3,-2],\ \ y_{above}=x^{2}-4, \ \ y_{below}=-x^{2}-2x$ $A_{1}=\displaystyle \int_{-3}^{-2}[(x^{2}-4)-(-x^{2}-2x)]dx$ $=\displaystyle \int_{-3}^{-2}[2x^{2}+2x-4 ]dx$ $= \displaystyle \left[ 2\cdot\frac{x^{3}}{3}+x^{2}-4x \right]_{-3}^{-2}$ $=2\displaystyle \cdot\frac{-8+27}{3}+(4-9)-4(-2+3)$ $=\displaystyle \frac{11}{3}$ For $x\in[-2,1],\ \ y_{above}=-x^{2}-2x,\ \ y_{below}=x^{2}-4$ $A_{2}=\displaystyle \int_{-2}^{1}[(-x^{2}-2x)-(x^{2}-4)]dx$ $=-\displaystyle \int_{-2}^{1}[2x^{2}+2x-4 ]dx$ $=-\displaystyle \left[ 2\cdot\frac{x^{3}}{3}+x^{2}-4x \right]_{-2}^{1}$ $=-(2\displaystyle \cdot\frac{1+8}{3}+(1-4)-4(1+2)$ $=9$ Total area = $A_{1}+A_{2}=\displaystyle \frac{11}{3}+9=\frac{38}{3}$
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