SOLUTION: The B & J co. wants to produce items at a minimum cost to the company. The cost of the items is modeled by the function C(x) = x^2 - 140 x + 5700, where x is the number of items pr

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Question 1031235: The B & J co. wants to produce items at a minimum cost to the company. The cost of the items is modeled by the function C(x) = x^2 - 140 x + 5700, where x is the number of items produced.
A.) How many items should the company produce to keep the cost to a minimum?
B.) What is the minimum cost?
C.) When would the company have a cost of $0?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+C%28x%29+=+x%5E2+-+140x+%2B+5700+
(a)
When the equation has the form:
+y+=+a%2Ax%5E2+%2B+b%2Ax+%2B+c+ , then the
x-value of the vertex ( max or min ) is:
+x%5Bmin%5D+=+-b%2F%282a%29+
-----------------------
In this case:
+a+=+1+
+b+=+-140+
+x%5Bmin%5D+=+-%28-140%29+%2F+%282%2A1%29+
+x%5Bmin%5D+=+70+
70 items should be produced to make
cost a minimum
-------------------------
(b)
Plug +x%5Bmin%5D+ into equation to get +C%5Bmin%5D+
+C%5Bmin%5D+=+70%5E2+-+140%2A70+%2B+5700+
+C%5Bmin%5D+=+4900+-+9800+%2B+5700+
+C%5Bmin%5D+=+800+
The minimum cost is $800
------------------------
When does +C%28x%29+=+0+?
+x%5E2++-+140x+%2B+5700+=+0+
+x%5E2+-+140x+=+-5700+
complete the square
+x%5E2+-+140x+%2B+%28+-140%2F2+%29%5E2+=+-5700+%2B+%28+-140%2F2+%29%5E2+
+x%5E2+-+140x+%2B+4900+=+-5700+%2B+4900+
+%28+x+-+70+%29%5E2+=+-800+
I can't take the square root of
both sides and get a real answer,
so the cost can never be zero
----------------------------
Here's the plot of +C%28x%29+:
+graph%28+400%2C+400%2C+-20%2C+140%2C+-240%2C+2400%2C+x%5E2+-+140x+%2B+5700+%29+