Question

Please help!!!
I would like to know what I am doing wrong, that my answer is different!!

Let C(x) =9x +25 be the cost to produce x units of a product, and let R(x)=-x^2+31x be the revenue. Find the maximum profit.
Why answer is 11?

Thnaks!! :)

Answer 1

what did you get?

Answer 2

I got 12

Answer 3

is this calculus or quadratic equations

Answer 4

Is Calculus.

Answer 5

maximize R(x) -C(x)

Answer 6

so your derivative is...?

Answer 7

-2x +........?

Answer 8

-2x+50+25?? I think this is the part that is wrong

Answer 9

hmm yeah...
R-C = -x^2 +22x +25

Answer 10

Ooh noo Sorry!!

Answer 11

whoops, should be:
R-C = -x^2 +22x -25

not that it matters much for our purposes...

Answer 12

so the derivative is -2x + 22

Answer 13

set it equal to zero and solve for x

Answer 14

that's your max.

Answer 15

I'm confused now, where do you get the 22 from?

Answer 16

derivative of 22x is 22

Answer 17

may be u should revise your notes on derivative properties before attemptig these word problems

Answer 18

cleared up @rocal2 ?
questions?

Answer 19

I am still trying to figure out why 22x?

Answer 20

-x^2 +31x -( 9x +25)

Answer 21

Yes, I got that part.. then next step: You substract 31x -(9x+25)

Answer 22

http://www.wolframalpha.com/input/?i=maximize+-x^2%2B31x+-+9x+-25
Profit = Revenue - Cost

Answer 23

profit is not 11, profit is 96 at x=11
http://www.wolframalpha.com/input/?i=-x^2%2B31x+-+9x+-25%2F.x-%3E11

Answer 24

I think they're asking for the number of units in order to maximize profit...

Answer 25

@experimentX I understand that, but I gonna have a test and I won't allow to use the internet, how do i get the 11? thats my question. ;))

Answer 26

find R-C
we did that... what was it?

Answer 27

@Algebraic! Yes they want the Maximum profit.

Answer 28

R-C= -x^2+22x+25

Answer 29

no they don't. not if the answer is 11. You're not reading the question properly or you're answering the wrong part of the question. anyway... right now we're finding the UNITS to be made so that profits are maximized...

Answer 30

R-C= -x^2+22x-25
now... find the location of the max by taking the derivative and setting it equal to zero

Answer 31

well ... i too suppose so.

Answer 32

-2x+22=0 ??

Answer 33

yes:)

Answer 34

solve for x?

Answer 35

Ok, good!! I undertand now I have to solve. But, the 22 can you explain me what you did?

Answer 36

" -x^2 " what's the derivative?

Answer 37

" 22x " what's the derivative?

Answer 38

So propably that is why i am lost!! I have to double check my notes.

Answer 39

you should be pretty familiar with straightforward and simple derivatives by now... especially if you're already doing optimization. definitely going to want to review the basic rules of differentiation for the test.

Answer 40

\[(x ^{n}) ' =n*x ^{n-1}\]
\[(c*x) ' = c\]

Answer 41

etc.

Answer 42

Ok, Yes that's true is an online class, and I have to teach myself. I will definately to go back and check... Thanks!