If the cost, C, for manufacturing x units of a certain product is given by c=x^2-5x+65, find the number of units manufactured at a cost of 13,865.

9514 1404 393

  120

Step-by-step explanation:

I find it pretty easy to obtain the solution by graphing ...

  c(x) -13865 = 0

The positive value of x that makes this so is x = 120.

120 units will have a cost of 13,865 to manufacture.

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If you like to solve this algebraically, you can probably do it most easily by completing the square.

  x^2 -5x = -65 +13865

  x^2 -5x +6.25 = 13806.25 . . . . . add the square of (-5/2)

  (x -2.5)² = 13806.25

  x -2.5 = √13806.25 = 117.5 . . . . only the positive square root is interesting

  x = 117.5 +2.5 = 120