hi, given f(x,y) = cos(x+y) - sin(x-y), find ∂f/∂x. is my work right? first, convert to cos x cos y - sin x sin y -sin x cos y + cos x sin y ∂f/∂x= -sin x cos y - cos x sin y - cos x cos y - sin x sin y or ∂f/∂x = -sin(x+y) - cos(x-y) which is right? thanks stupid