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707miranda

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**[SOLVED] differentiation of cos(x)cos(y) or sin(x)sin(y)**

## Homework Statement

Determine if the equation is exact, if exact solve.

[cos(x)cos(y)+2x]dx-[sin(x)sin(y)+2y]=0

## Homework Equations

I have forgotten how to take the derivative of cos(x)cos(y) or sin(x)sin(y). Is this a product rule thing, or is it the chain rule?

## The Attempt at a Solution

I understand that if

$$\frac{\partial M}{\partial y}=\frac{\partial N}{\partial x}$$

then the equation is exact and you can integrate M w/respect to x and N w/respect to y and combine the similar terms for the solution f(x,y)=solution.

Here $$\frac{\partial M}{\partial y}\neq\frac{\partial N}{\partial x}$$

because the derivative of sin is cos and the derivative of cos is -sin. So while I know the equation isn't exact. I'm still bugged about the whole derivative thing.

Thanks in advance geniuses O o O ><((<))">

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