Question

The total revenue R = 720 - 3x² where x is number of items sold. Find x for which total  revenue R is increasing.

Answer 1

R = 720x - 3x²

`(dR)/(dx)` = 720 - 6x
Total revenue R is increasing if `(dR)/(dx)` > 0.
i.e; if 720 - 6x > 0
     if 720 > 6x
i.e; if 120 > x
∴ R is increasing for 120 > x.