t*sin^3(t) dt.求积分啊.
题目
t*sin^3(t) dt.求积分啊.
答案
sin^3(t) = [1-cos(2t)] sint / 2 = (3/4)sint - (1/4) sin(3t)
I = (3/4) ∫ t d(-cost) + (1/12) ∫ t d(cos3t)
= (-3/4) [ t cost - ∫ cost dt ] + (1/12) [ t cos(3t) - ∫ cos(3t) dt ]
= (-3/4) [ t cost - sint] + (1/12) [ t cos(3t) - (1/3) sin(3t) ] + C
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