Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 15 - Multiple Integrals - 15.3 Exercises - Page 1019: 22

Answer

$\frac{7}{4}$

Work Step by Step

The region $D$ can be defined as $D = \{(x,y)| 0\leq x \leq 1, 2x \leq y \leq 3-x \}$ Now, we rewrite our integral as $\int_0^1\int_{2x}^{3-x} 2xy \ dydx$ Integrating with respect to y, we get $\int_0^1 [xy^2]^{3-x}_{2x} \ dx$ Plugging in the limits, we get $\int_0^1 x(3-x)^2 - x(2x)^2 \ dx$ Expanding and combinging like terms gets us $\int_0^1 -3x^3 -6x^2 + 9x \ dx$ Integrating with respect to x, we get $[-\frac{3}{4}x^4-2x^3+\frac{9}{2}x^2]^1_0$ Plugging in the bounds, we get $-\frac{3}{4}(1)^4-2(1)^3+\frac{9}{2}(1)^2 - (-\frac{3}{4}(0)^4-2(0)^3+\frac{9}{2}(0)^2) = -\frac{3}{4}-2+\frac{9}{2} = \frac{7}{4}$
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