Prove FT^2(f(x))=f(-x): Answers & Tips

liorda
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Prove: FT^2(f(x))=f(-x) where FT is the Fourier transform.

I tried to change x into -x' but with no success.

Do I need to separate cases for even f and odd f?
 
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You just need to realize that e.g., integral(exp(i*k*t1)*exp(i*k*t2)*dk) is proportional to delta(t1+t2).
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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