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问题: 用第二换元积分法计算

∫dx/[x^2√(1-x^2)]

解答:

令x=sint (-pi/2<t<pi/2)则√(1-x^2)=cost,dx=costdt

∫dx/[x^2√(1-x^2)]
=∫costdt/[(sint)^2cost]
=∫dt/(sint)^2
=-cott+C
=-cost/sint+C
=-(1/x)√(1-x^2)+C.