x²arctanx的2021阶导数

1、y'=(x^2)'*arctanx+x^2*(arctanx)'

=2x*arctanx+x^2/(1+x^2)

2、y'=(cos^3x)'/(cos^3x)

=3cos^2x*(-sinx)/(cos^3x)

=-3sinx/cosx

=-3tanx