用分部积分就可以算出来
∫t cos²t dt = 1/2∫t(cos 2t - 1)dt
=1/2∫t cos2t -1/2∫tdt
1/2∫tdt = -1/4
1/2∫t cos2t dt = 1/4∫t dsin2t = 1/4t sin2t|(1→0) - 1/4∫sin2t dt
=-1/4sin2 + 1/8cos2t|(1→0)
=-1/4sin2 + 1/8(1-cos2)
所以积分的结果是
-1/4sin2 -1/8cos2 -1/8