Fourier coefficients

[akleron]

Hello every one!
im trying to prove the following question but honestly I am new to the subject and kind off clueless..
Would love some help!

The question




I tried to show equality but failed.

 

[Steven G]

Where did you get those two equations from? What happened to the negative sign? How did you factor out e^(pi/2)?

You do know that the prerequisite for being able to do these problems is arithmetic.