换元t=arcsinx=∫t/cos³tdsint=∫tdtant=ttant-∫tantdt=ttant+ln|cost|+C
令x=sint，dx=costdt原式=∫t/cos²tdt=∫tdtant=ttant－∫tantdt=ttant－∫sint/costdt=ttant－∫1/costdcost=ttant－ln|cost|+C
