If we let u = 2x3 - 1 then y = u4.

So now

To find the derivative of such an expression, we can use our new rule:

`d/(dx)u^n=n u^(n-1)(du)/(dx`

where u = 2x3 − 1 and n = 4.

So

`(dy)/(dx)=n u^(n-1)(du)/(dx)`

`=[4(2x^3-1)^3][6x^2]`

`=24x^2(2x^3-1)^3`

We could, of course, use the chain rule, as before:

`(dy)/(dx)=(dy)/(du)(du)/(dx`