x=sint,t∈[-π/2,π/2]∫√(1-x²)dx=∫costdsint=∫cos²tdt=tcos²t+∫sin2tdt=tcos²t-cos2t/2+c=t-tsin²t+sin²t-1/2+c=(1-x²)arcsinx+x²+c'
(1-x^2)^1/2时,设x=sect太麻烦 应设x=sint (-π/2,π/2)或x=cost (π,0) 方便计算就不用说了