Current in an ac circuit is given by I=3sinωt+4cosωt , then

i=3sinωt+4cosωt =5[35sinωt+45cosωt]=5[sin(ωt+δ)]Rms value=52Root Mean square  value =∫T1T2i2dt∫T1T2dtThe initial value is not given hence the mean value will be different for various time intervals. If voltage applied is V=Vmsinωt  then I given by equation (i) indicates that it is ahead of V by δ where which indicates that the circuit contains R and C.