While reading in Signals book, here's what I read:(adsbygoogle = window.adsbygoogle || []).push({});

I=1/2 [(integral sign) cos(n+m)wt dt + (integral sing) cos (n-m)wt dt]

"Because cos wt executes one complete cycle during any interval of duration T, cos (n+m)wt executes (n+m) complete cycles during any interval of duration T. Therefore the first integral in the above equation, which represents the area under n+m complete cycles of a sinusoid, equals zero. The same argument shows that the second integral in the above equation is also zero, except when n=m. Hence I in the above equation is zero for all n is not equal to m."

My question is: How do these integrals become zero?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# How does this integral become zero?

**Physics Forums | Science Articles, Homework Help, Discussion**