Question

Find a potential function for F or determine that F is not conservative. (If F is not conservative, enter NOT CONSERVATIVE.) F = cos(z), 10y, - x sin(z)

Answer 1

For $F$ to be conservative, we need to have

$\dfrac{\partial f}{\partial x}=\cos z$

$\dfrac{\partial f}{\partial y}=10y$

$\dfrac{\partial f}{\partial z}=-x\sin z$

Integrate the first PDE with respect to $x$:

$\displaystyle\int\frac{\partial f}{\partial x}\,\mathrm dx+\int\cos z\,\mathrm dx\implies f(x,y,z)=x\cos z+g(y,z)$

Differentiate with respect to $y$:

$\dfrac{\partial f}{\partial y}=10y=\dfrac{\partial g}{\partial y}\implies g(y,z)=5y^2+h(z)$

Now differentiate $f$ with respect to $z$:

$\dfrac{\partial f}{\partial z}=-x\sin z=-x\sin z+\dfrac{\mathrm dh}{\mathrm dz}\implies\dfrac{\mathrm dh}{\mathrm dz}=0\implies h(z)=C$

So we have

$f(x,y,z)=x\cos z+5y^2+C$

so $F$ is indeed conservative.