Signals and Systems - Engineering

Q1:

For the wave i = I0 + I1m sin ωt + I3m sin 3ωt, the rms value is

A I = (I20 + I21m + I23m)0.5

B

C I = 0.707 (I20 + I21m + I23m)0.5

D none of these

ANS:B -

How please explain?