The problem: Determine the derivative of the following function
$f(z)=\cos(x) \cosh(y)-i \sin(x) \sinh(y)$
The original exercise can be found at 2.17 (e) page 36
Should i try to rewrite the function in terms of $z=x+iy$ or is there some connection between the partial derivatives and the complex derivative that I am missing?
Thanks @Claude Leibovici
The equations needed are:
$(1) \cos(a+b) = \cos(a)\cos(b)-\sin(a)\sin(b)$
With (2) and (3) I can rewrite the cosh and sinh in terms of cos and sin.
Then I can use (1) to combine it into one cos.