\[\frac{d}{dx} {(\cos{({x}^{3})})}^{2}\]

1
Remove parentheses.
ddxcos2x3\frac{d}{dx} \cos^{2}{x}^{3}

2
Use Chain Rule on ddxcos2x3\frac{d}{dx} \cos^{2}{x}^{3}. Let u=cos(x3)u=\cos{({x}^{3})}. Use Power Rule: dduun=nun1\frac{d}{du} {u}^{n}=n{u}^{n-1}.
2cos(x3)(ddxcos(x3))2\cos{({x}^{3})}(\frac{d}{dx} \cos{({x}^{3})})

3
Use Chain Rule on ddxcos(x3)\frac{d}{dx} \cos{({x}^{3})}. Let u=x3u={x}^{3}. Use Trigonometric Differentiation: the derivative of cosu\cos{u} is sinu-\sin{u}.
2cos(x3)×sin(x3)(ddxx3)2\cos{({x}^{3})}\times -\sin{({x}^{3})}(\frac{d}{dx} {x}^{3})

4
Use Power Rule: ddxxn=nxn1\frac{d}{dx} {x}^{n}=n{x}^{n-1}.
6x2cos(x3)sin(x3)-6{x}^{2}\cos{({x}^{3})}\sin{({x}^{3})}

Done

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