y=cos3次方x求导数啊

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y=cos3次方x求导数啊
y=cos3次方x求导数啊

y=cos3次方x求导数啊
{cos^3 (3x)}'
= 3 cos^2(3X) {cos(3x)}'
= 3 cos^2(3X) {-sin(3x)} (3x)'
= 3 cos^2(3X) {-sin(3x)} 3
= -9 sin(3x) cos^2(3x)

[cos^3 (x)]'
= 3 cos^2(x)[cos(x)]'
= 3 cos^2(x)*(-sin(x))
=- 3/2* cosx*sin(2x)