# Math Help - Math Helpp

1. ## Math Helpp

Find the value of the second derivative when x = 20 for
the following function:

f(x) = 200x divided by (x+40)

2. did you find the first derivative?

3. f(x) = 200x divided by (x+40)

=> f(x) = \frac{200x}{x+40}

=> f'(x) = \frac{200(x+40)-1*200x}{(x+40)^2}

...

=> f''(x) =

4. Originally Posted by Rapha
f(x) = 200x divided by (x+40)

=> f(x) = \frac{200x}{x+40}

=> f'(x) = \frac{200(x+40)-1*200x}{(x+40)^2}

...

=> f''(x) =
why didn't you simplify f'(x) ?

$f'(x) = \frac{200(x+40)-1(200x)}{(x+40)^2}$

$f'(x) = \frac{200x + 8000 - 200x}{(x+40)^2}$

now finish the algebra clean-up for f'(x) and find f''(x).

5. Originally Posted by skeeter
why didn't you simplify f'(x) ?
i think it is his business, because simplify f'(x) is duck soup, isn't it?