An ac voltage is given by e=3+4sin(wt+π/3). Calculate the rms value of voltage

The effective value is the RMS value. Let’s work this out for any combination of DC plus AC, ie: for  a+bsin⁡(ωt). 

The square of this is: 

a² + 2 a b sin ⁡ ( ω t ) + b² sin² ( ω t ) 

Using the trig identity  sin² ( x ) =( 1/ 2) ( 1 − cos ⁡ ( 2 x ) ) 

this becomes:  a² + 2 a b sin ⁡ ( ω t ) + b²/ 2 ( 1 − cos ⁡ ( 2 ω t ) ) 

Next we need to take the mean. However both sine and cosine have a mean of zero and so we can ignore these terms, leaving us with a mean of simply:  a² + b² / 2  As this is constant then the mean has the same value. Finally we take the root, giving the RMS value: