Question

A profit of a football club after a takeover is modeled by p(t) = t3 - 14t2 + 20t + 120, which t is the number of years after the takeover. In which years was the club making loss?

Answer 1

T = 5, so after 5 years
p(t) = t^3 - 14t^2 + 20t + 120

Take derivative to find minimum:
p’(t) = 3t^2 - 28t + 10

Factor to solve for t:
p’(t) = (3t - 2)(t - 5)
0 = (3t - 2)(t - 5)

0 = 3t - 2
2 = 3t
2/3 = t

Plug 2/3 into original equation, this is a maximum. We want the minimum:

0 = t - 5
5 = t

Plug back into original:
5^3 - 14(5)^2 + 20(5) + 120
125 - 14(25) + 100 + 120
125 - 350 + 220
- 225 + 220
p(5) = -5