Tokyo-Moto Quad Racers found that its daily profit, P, in thousands, is given by
P = -7x2 + 84x - 198

where x is the number of Quad Racers manufactured daily. Which of the following is the best estimate for the maximum profit the manufacturer can earn per day, in thousands?

Question

Tokyo-Moto Quad Racers found that its daily profit, P, in thousands, is given by 
P = -7x2 + 84x - 198

where x is the number of Quad Racers manufactured daily. Which of the following is the best estimate for the maximum profit the manufacturer can earn per day, in thousands?

anonymous · Answer

You can find the max and min by taking the derivative and setting it to zero.
Take that value and plug it into the 2nd derivative, if you get a negative number, then it is a max and if it is positive, then it is a min.
The first derivative here is -14x+84, set it equal to zero and solve for x, then continue with the steps.