问一道不定积分的题目求(arctanx)^2的原函数
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问一道不定积分的题目
求(arctanx)^2的原函数
求(arctanx)^2的原函数
用分部积分法
∫(arctanx)^2dx
=x(arctanx)^2-∫[x*2arctanx*(1/1+x^2)]dx
=x(arctanx)^2-∫[2x/(1+x^2)]arctanxdx
再对∫[2x/(1+x^2)]arctanxdx先换元,再分部积分:
令u=arctanx,du=1/(1+x^2)
x=tanu,2x=2tanu
∫[2x/(1+x^2)]arctanxdx
=∫2utanudu
=∫tanud(u^2)
=u^2tanu-∫u^2/(1+u^2)du
=u^2tanu-∫(u^2+1-1)/(u^2+1)du
=u^2tanu-∫[1-1/(1+u^2)]du
=u^2tanu-u+arctanu
=x(arctanx)^2-arctanx+tanx+C
原式
=x(arctanx)^2-x(arctanx)^2+arctanx-tanx+C
∫(arctanx)^2dx
=x(arctanx)^2-∫[x*2arctanx*(1/1+x^2)]dx
=x(arctanx)^2-∫[2x/(1+x^2)]arctanxdx
再对∫[2x/(1+x^2)]arctanxdx先换元,再分部积分:
令u=arctanx,du=1/(1+x^2)
x=tanu,2x=2tanu
∫[2x/(1+x^2)]arctanxdx
=∫2utanudu
=∫tanud(u^2)
=u^2tanu-∫u^2/(1+u^2)du
=u^2tanu-∫(u^2+1-1)/(u^2+1)du
=u^2tanu-∫[1-1/(1+u^2)]du
=u^2tanu-u+arctanu
=x(arctanx)^2-arctanx+tanx+C
原式
=x(arctanx)^2-x(arctanx)^2+arctanx-tanx+C