I am being asked to find the derivative by what I think is the chain rule of this equation:

$\displaystyle (x^2+2)^2$

Let u be:

$\displaystyle u=(x^2+2)^2$

This is the part I am having trouble understanding. The formula for the derivative of $\displaystyle u^2$ is given as:

$\displaystyle \frac{d}{dx}u^2=\frac{du}{dx}\frac{d}{du}u^2=(2x)( 2u)=4x(x^2+2)$

Is that the chain rule? How was $\displaystyle (2x)(2u)$ calculated?

Thanks in advance...