Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 16 - Section 16.3 - The Fundamental Theorem for Line Integrals - 16.3 Exercise - Page 1152: 20

Answer

$-1$

Work Step by Step

Vector field $F(x,y) = $ $(1+xy)e^{xy}i$ + $x^{2}e^{xy}j$ Since $F(x,y)$ is assumed conservative, we have $f_{x} = (1+xy)e^{xy}$ $f_{y} = x^{2}e^{xy}$ Thus, integrating $f_{x}$ with respect to x, we get $f = xe^{xy} + g(y)$ [g(y) : is a function of y] Now taking the derivative of $f$ with respect to y, we get $f_{y} = x^{2}e^{xy} + g'(y)$ Since $f_{y} = x^{2}e^{xy}$ and $f_{y} = x^{2}e^{xy} + g'(y)$, we now get $g'(y) = 0$ Therefore, $f = xe^{xy}$ Using the fundamental theorem of line integrals $\int_C \nabla f \cdot dr = f(r(b)) - f(r(a)) $ , The curve $C$ is defined by the parameter $r(t) = \cos(t)i + 2\sin(t)j$, $0≤t≤\pi/2$ Thus, we get $r(b) = r(\pi/2)$ $r(a) = r(0)$ Hence, $r(b) = (0,2)$ and $r(a) = (1,0)$, and we can then get $f(0,2) - f(1,0) = 0 - 1 = -1$
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