帮忙求一道关于反三角函数二阶导数的问题?y=arctan（x+y）这个是题~

Question

帮忙求一道关于反三角函数二阶导数的问题?
y=arctan（x+y）这个是题~

Answer 1

(arctanx)'=1/(1+x^2)对y求导：y'=[arctan（x+y）]'=1/[1+(x+y)^2](x+y)'=1/[1+(x+y)^2](1+y')y'[1+(x+y)^2]=1+y'y'=1/(x+y)^2y''=-2/(x+y)^3*(x+y)'=-2(1+y')/(x+y)^3=-2[1+1/(x+y)^2]/(x+y)^3=-2[1/(x+y)^3+1/(x+y...