The profit of a company can be modeled using the rule P = -C2 + 10C - 16 where P represents the profit and C represents the cost of the item sold.
What cost will produce the maximum profit?
This makes little sense but anyway:
c^2 - 10 c + 16 = - p
c^2 - 10 c = - p - 16
c^2 - 10 c + 25 = -p + 9
(c-5)^2 = - (p-9)
max at c = 5 and p = 9