Question:

The diagram shows the curve , where k is constant. The curve has a minimum point on the x-axis.

(i) Find the value of .

(ii) Find the coordinates of the maximum point of the curve.

(iii) State the set of values of for which is a decreasing function of .

Attempt:

(i)

(ii)

(iii) I don't know how to get the decreasing order?!...