fx(x+1)^(1/2)dx 设x+1)^(1/2)=t x=t^2-1 dx=2t 原式=f(t^2-1)t*2tdt =2f(t^4-t^2)dt =2(t^5/5-t^3/3)+C =2/5(x+1)^(5/2)-2/3t^3+C fxdx/(1+x^2)^2 设x=tant x^2=tan^2t 1/x^2=cot^2t 1/x^2+1=csc^2t=1/sin^2t sin^2t=x^2/(x^2+1) dx=sec^2tdt
把所给变量取值带人方程计算
1看是否满足约束条件
2看哪个解最优