(sinx)^4=[(1-cos2x)/2}^2=(1-2cos2x)/4+(cos2x)^2
=(1-2cos2x)/4+(cos4x+1)/2=3/4-(1/2)cos2x+(1/2)cos4x
∫(SINX)^4dx=(3/4)x+(1/4)sin2x-(1/8)sin4x