Question

3.If y=80x-16x2, find the difference ∆y-dy if x=4 and ∆x=-0.2

Answer 1

$$y=80x-16x^2$$

$$\dfrac{dy}{dx}=y'=80-32x$$

$$y'(4)=80-32(4)=-48$$

$$\Delta y=-48(-0.2)=9.6$$