Derivative of $(5x-2)^3$ How is the derivative of $(5x-2)^3$ equal to $15(5x-2)^2$ and not $3(5x-2)^2$. According to $\frac{df}{dx} = nx^{n-1}$, it has to be $3(5x-2)^2$ right. Please explain.

You simply forgot to remember using the chain rule:
\begin{align}
\frac{d}{dx}(5x-2)^3 = 3(5x-2)^2 \frac{d}{dx}(5x-2) =3(5x-2)^2 \cdot 5 = \boxed{15(5x-2)^2}
\end{align}
