∫(cosΘ)^4dΘ
=∫(1+cos2Θ)^2/4 dΘ
=∫[1+2cos2Θ+(cos2Θ)^2]dΘ/4
=Θ/4+sin2Θ/4+∫(1+cos4Θ)dΘ/8
=3Θ/8+sin2Θ/4+sin4Θ/32+C