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: 38

Answer

$16$

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 $x\in[-2,0],\ \ y_{above}=2x^{3}-x^{2}-5x,\ \ y_{below}=-x^{2}+3x$ $A_{1}=\displaystyle \int_{-2}^{0}[(2x^{3}-x^{2}-5x)-(-x^{2}+3x)]dx$ $=\displaystyle \int_{-2}^{0}(2x^{3}-8x)dx$ $= \displaystyle \left[ 2\cdot\frac{x^{4}}{4}-4x^{2} \right]_{-2}^{0}$ $=\displaystyle \frac{0-16}{2}-4(0-4)$ $=8$ For $x\in[0,2],\ \ y_{above}=-x^{2}+3x,\ \ y_{below}=2x^{3}-x^{2}-5x$ $A_{2}=\displaystyle \int_{0}^{2}[(-x^{2}+3x)-(2x^{3}-x^{2}-5x)]dx$ $=-\displaystyle \int_{0}^{2}(2x^{3}-8x)dx$ $= -\displaystyle \left[ 2\cdot\frac{x^{4}}{4}-4x^{2} \right]_{0}^{2}$ $=-[\displaystyle \frac{16-0}{2}-4(4-0)]$ $=8$ Total area = $A_{1}+A_{2}= 8+8=16$
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