求一个不定积分∫dx/[(x^2)√(a^2+x^2)] (其中a>0)的解题步骤

x=atant
t=arctan(x/a)
dx=asec²tdt
√(a²+x²)=asect
原式=∫asec²tdt/(a³tan²tsect)
=∫sectdt/(a²tan²t)
=∫(1/cost)dt/(a²sin²t/cos²t)
=(1/a²)∫(cost/sin²t)dt
=(1/a²)∫(1/sin²t)d(sint)
=(-1/a²)∫(-1/sin²t)d(sint)
=-(1/a²)(1/sint)+C
=-csc[arctan(x/a)]/a²+C