If f(x)=cos(x)cos(2x)cos(4x)…cos(2nx)f(x) = \cos(x) \cos(2x) \cos(4x) \dots \cos(2^n x)f(x)=cos(x)cos(2x)cos(4x)…cos(2nx), what is f′(0)f'(0)f′(0)?
000
111
−1-1−1
2n2^n2n