dy=2tan(1+2x^2)*[sec(1+2x^2)]^2*4xdx
dy=8xtan(1+2x^2)sec(1+2x^2)]^2dx
=8x*sin (1+2x^2)[sec(1+2x^2)]^3dx.2tan(1+2x^2)这个是怎么求出来的