\text { (a) Given that } \mathrm{f}(x)=x^{2}-4 x \text {, use differentiation from first principles to show that } \mathrm{f}^{\prime}(x)=2 x-4 \text {. } \text { (b) Find the equation

of the curve through }(2,7) \text { for which } \frac{\mathrm{d} y}{\mathrm{~d} x}=2 x-4