Find dy/dx of y=(cosx)^x
d/dx of a^u=lna*a^u*u'
The Attempt at a Solution
I thougt I just had to follow the form shown above, and this is what I got.
However, the actual answer is (cosx)^x*(ln(cosx)-xtanx)
I don't understand where this comes from at all. Thanks for your input.