Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 16 - Section 16.3 - The Fundamental Theorem for Line Integrals - 16.3 Exercise - Page 1094: 5

Answer

Conservative $f(x,y)=ye^{xy} + K$

Work Step by Step

Given: $F(x,y)=y^2e^{xy}i+(1+xy)e^{xy}j$ If $F(x,y)=Ai+Bj$ is a conservative field, then throughout the domain $D$, we get $\dfrac{\partial A}{\partial y}=\dfrac{\partial B}{\partial x}$ Here, $A$ and $B$ are first-order partial derivatives on the domain $D$. Then, we have $A_y=2ye^{xy}+xy^2e^{xy}; B_x=2ye^{xy}+xy^2e^{xy}$ Here, $\dfrac{\partial A}{\partial y} = \dfrac{\partial B}{\partial x}$ Thus, the vector field $F(x,y)$ is conservative. Next, we will find $f$ such that $F=\nabla f$ Here, we have $f_x=y^2e^{xy}..(1) \\ f_y=(1+xy)e^{xy} ...(2)$ Now, integrate $f_x$ with respect to $x$, so we get $f(x,y)=ye^{xy}+g(y)$ ...(3) Here, $g(y)$ represents a constant of integration with respect to $x$ with a function of $y$. Now, we will differentiate $f(x,y)=ye^{xy}+g(y)$ with respect to $y$. $f_y(x,y)=yxe^{xy}+e^{xy}+g'(y) ...(4)$ On comparing the equations (2) and (4) , we get $g'(y)=0$ Now, $g(y)=K$ [ Integrate with respect to $y$] Here, $K$ is a constant. Hence, the function $f(x,y)$ becomes: $f(x,y)=ye^{xy}+k$
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