SOLUTION: The cost in millions of dollars for a company to manufacture x thousand automobiles is given by the function C(x)=4x^2-24x+81. Find the number of autromobiles that must be produced

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Question 427096: The cost in millions of dollars for a company to manufacture x thousand automobiles is given by the function C(x)=4x^2-24x+81. Find the number of autromobiles that must be produced to minimize cost.
Answer key states 3,000.

Found 2 solutions by ewatrrr, htmentor:
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!

Hi
The cost in millions of dollars for a company to manufacture x thousand
automobiles is given by the function C(x)=4x^2-24x+81.
Find the number of autromobiles that must be produced to minimize cost.
4x^2-24x+81 |parabola opening upward. completing the square to find the vertex
c(x)= 4[(x-3)^2 -9] + 81
c(x)= 4(x-3)^2 - 36 + 81
c(x)= 4(x-3)^2 + 45 Vertex(3,45) x= 3 OR 3000 automobiles

Answer by htmentor(1343) About Me  (Show Source):
You can put this solution on YOUR website!
C%28x%29=4x%5E2-24x%2B81
This function will have a minimum where dC(x)/dx = 0
Taking the derivative, and setting = 0, we have 8x+-+24+=+0
Solving for x gives, x = 3
So the answer is 3000 automobiles
Here is the graph of the function:
graph%28300%2C200%2C-10%2C10%2C-100%2C100%2C4x%5E2-24x%2B81%29