last question for today...it's about application in economics..
suppose a company has a marginal cost function y = C' x√(9+x²), where x is the number of thousands of items sold and the cost C is in thousand of dollar. if fixed cost are $11 thousand, what is the total cost of manufacturing the first 4 thousand items?
I used intergration to find the C(x) then I substitute x=4 and C= 11.. is that correct?

Question

anonymous · Answer

C'= x√(9+x²) 

you mean?

anonymous · Answer

that is marginal cost

anonymous · Answer

sorry.. c'(x)=x√(9+x²) 
yeah..

anonymous · Answer

yes, integrate marginal cost to get total cost; use u-sub

anonymous · Answer

is that correct when i subs C=11?

anonymous · Answer

integrated out to be

1/3 (x^2+9)^(3/2)+c

anonymous · Answer

1/3 (4^2+9)^(3/2)+11

anonymous · Answer

i got 2/3 (9 + x^2)^(3/2) + C

anonymous · Answer

u=x^2+9

du=2x dx

               $$1/2\int \sqrt{u} du$$

anonymous · Answer

oh.. i forgot that.. thanks.. (: