a) to find use the formula given

to find first find by differentiating with respect to x.

you use value of to find

b) If the x-axis is to be a tangent of the curve you require that and for some value of x. so you must determine whether has any real solutions.

c) This is basic application of formula.

use your values form part a) to do this.

d) Like part c) this is just application of the formula where

Bobak