原式=(1/4)∫(1+cos2x)^2dx
=(1/4)∫[1+2cos2x+(cos2x)^2]dx
=x/4+(sinx)/4+(1/8)∫(1+cos4x)dx
=x/4+(sinx)/4+x/8+(sin4x)/32+C
=3x/8+(sinx)/4+(sin4x)/32+C