Divide by 2

C=x^{2}-160x+6,010

Take the first derivative

C'=2x-160 set it equal to zero 2x-160=0

divide by 2: x-80=0 or x=80

The cost function is an equation which graphed is a parabola. It's minimum point is where the slope equals zero. That's the point where the first derivative equals zero.

At x=80 cost = 6400-12800+6,010= -390 This negative cost is profit.

Or you could algebraically solve the quadratic equation a=2,

b=-320

c=12020

plug into the quadratic formula x=1/2a(-b + or - square root of b^{2}-4ac)

=1/4(320 + or - square root of 320^{2} - 4(2)(12020)) = 1/4(320 + or - square root of 6,240)

=80 + or - square root of 6240

=80 + or - almost 79 = approximately 1 or 159

80 is the midpoint, with 1 or 159 as the break even points where cost=revenues and profit =0

80 is maximum profit or minimum cost

Plug 80 into the original cost equation, and you get the minimum cost or maximum profit.