# Derivative of cos cube x | Cos^3x Derivative

The derivative of cos cube x (cos^3x) is equal to -3cos2x sinx. In this post, we will find the derivative of cos cube x using the chain rule.

The derivative formula of cos3x is given as follows:

d/dx (cos3x) = -3cos2x sinx.

## Derivative of Cos^3x

Explanation:

As cos3x is a composite function, we will use the chain rule to find its derivative. To do so, let us put

u = cosx.

Thus, cos3x = u3.

As u=cosx, we have that du/dx = -sinx.

Now, by the chain rule the derivative of cos cube x will be equal to

$\dfrac{d}{dx}$ (cos3x) = $\dfrac{d}{dx}$ (u3)

= $\dfrac{d}{du}$ (u3) × $\dfrac{du}{dx}$

= 3u2 × (-sinx) by the power rule of derivatives: d/dx (xn) =nxn-1.

= – 3cos2x sinx.

So the derivative of cos3x (cos cube x) is equal to – 3cos2x sinx, that is, d/dx (cos3x) = -3cos2x sinx which is proved by the chain rule of derivatives.

## FAQs

Q1: What is the derivative of cos3x?

Answer: The derivative of cos3x (cos cube x) is – 3cos2x sinx.

Q1: If y=cos3x, then find dy/dx?

Answer: If y=cos3x, then dy/dx = -3cos2x sinx.