换元法求积分用换元法

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换元法求积分用换元法

换元法求积分用换元法
换元法求积分

用换元法

换元法求积分用换元法
设 x = 2t,则 dx = 2dt
∫dx/(1-cosx)
=∫2dt/(1-cos2t)
=∫2dt/[2(sint)^2]
=∫dt/(sint)^2
=∫(csct)^2*dt
=-cot(t) + C
=-cost/sint + C
=-2(cost)^2/[2sint*cost] + C
=-(1+cos2t)/sin2t + C
=-1/sin2t - cos2t/sin2t + C
=-csc2t - cot2t + C
=-cscx - cotx + C
所以,答案是 D