I am having trouble showing the following and i was wondering if anyone can point out my mistake.
let f be a 2pi periodic function and
$f_m(t)=f(mt)$
show the n-th fourier coefficient
$\hat{f_m}(n)=\hat{f}(n/m)$ if m divides n $\hat{f_m}(n)=0$ if m does not divides n
my attempt:
$\hat{f_m}(n)=\frac{1}{2\pi}\int_0^{2\pi}f(mt)e^{-int}dt$
substitute x=mt we get
$=\frac{1}{2\pi}\int_0^{2\pi}f(x)e^{-i\frac{n}{m}x}\frac{dx}{m}$
as you can see, im having a extra m on the denominator. Furthermore, i do not see why it should equal 0 if m does not divide n