3.6: Differentiation, small increments and connected rates

Find $\dfrac{\mathrm{d}y}{\mathrm{d}x}$.

Hence find the approximate change in $y$ when $x$ increases from $2$ to $2 + h$, where $h$ is small.

At the instant when $x = 2$, $y$ is increasing at $4$ units per second. Find the corresponding rate of increase in $x$.