Thread: Find the number c that satisfies the conclusion of the mean value theorem.

f(x) = x / (x+ 4) [1,8]

I found fprime(x) to be 4/(x+4)^2
Then I used (f(b) - f(a)) / (b -a) and found that to be 7/15

I set the equation to zero to solve for c and my answer comes out wrong. (squarroot60/7)-4
PS How do I use the math syntax keys on this forum?

Pretty sure f(b) - f(a) equals 7/15 here. When you divide by (b-a), you get 1/15.

The derivative looks good.

I hope this helps! Good luck!

Set what equation to 0? The mean value theorem says that there exist some c such that


f(8)- f(1)= 7/15. (f(8- f(1)/(9- 1)= 1/15. You want to set .

2/7 ?

still not sure what I'm doing wrong, the answer i submit is wrong :/

HallsofIvy was correct up until this point:

You want to set

You actually want to set

[EDIT]: I'm sure that was a "thought-o" on HallsofIvy's part.

??

Your answer is correct. I would show the steps of rejecting the inadmissible solution when you take the square root.

I think you're done!