数学求不定积分∫1/1+√(X+2)dx
设u=1+√(X+2),则√(X+2)=u-1 ,du=dx/[2√(X+2)]=dx/[2(u-1)]
就是：dx=[2(u-1)]du,
所以,原式=∫2(u-1)du/u=∫2du-∫2du/u
=2u-2Ln|u|+C1
=2[1+√(X+2)]-2Ln|1+√(X+2)|+C1
=2+2√(X+2)-2Ln|1+√(X+2)|+C1
=2√(X+2)-2Ln|1+√(X+2)|+C