Thomas' Calculus 13th Edition

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

Chapter 5: Integrals - Section 5.4 - The Fundamental Theorem of Calculus - Exercises 5.4 - Page 287: 47

Answer

$\frac{28}{3}$

Work Step by Step

Step 1. Given the function $y=-x^2-2x=-x(x+2)$ and the interval $[-3,2]$, find the zeros at $x=-2,0$; thus we need to divide the integration into three regions: $[-3,-2],[-2,0],[0,2]$ Step 2. We have $A_1=\int_{-3}^{-2}(-x^2-2x)dx=(-\frac{1}{3}x^3-x^2)|_{-3}^{-2}=(-\frac{1}{3}(-2)^3-(-2)^2)-(-\frac{1}{3}(-3)^3-(-3)^2)=-\frac{4}{3}$ Step 3. Similarly, $A_2=\int_{-2}^{0}(-x^2-2x)dx=(-\frac{1}{3}x^3-x^2)|_{-2}^{0}=(-\frac{1}{3}(0)^3-(0)^2)-(-\frac{1}{3}(-2)^3-(-2)^2)=\frac{4}{3}$ Step 4. For the third part, $A_3=\int_{0}^{2}(-x^2-2x)dx=(-\frac{1}{3}x^3-x^2)|_{0}^{2}=(-\frac{1}{3}(2)^3-(2)^2)-(-\frac{1}{3}(0)^3-(0)^2)=-\frac{20}{3}$ Step 5. The total area is given by $A=|A_1|+|A_2+|A_3|=\frac{28}{3}$
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