[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...