求tan平方t的导数

令y=tan^2(t) 则y ' =[(sin^2 t )/(cos^2 t )] '=[1/(cos^2 t) -1] ' =[1/(cos^2 t)] ' =-sint *(-2)/(cos^3 t) =2sint / (cos^3 t)即y '=2sint / (cos^3 t)