(adsbygoogle = window.adsbygoogle || []).push({}); [SOLVED] differentiation of cos(x)cos(y) or sin(x)sin(y)

1. The problem statement, all variables and given/known data

Determine if the equation is exact, if exact solve.

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

2. Relevant 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?

3. 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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# Homework Help: Differentiation of cos(x)cos(y) or sin(x)sin(y)

**Physics Forums | Science Articles, Homework Help, Discussion**