Originally Posted by

**transgalactic** i got a solution to this..but i cant understand it.

they make mean value theorem on f'(x) [x1,x2] so x2>=x1

$\displaystyle

\frac{f'(x_2)-f'(x_1)}{x_2-x_1}=f'(c)

$

$\displaystyle

|f'(x_2)-f'(x_1)|=|f'(c)||x_2-x_1|

$

then they say that by the second law of weirsstas there is a minimum and maximum

so there is l,L on [a,b] so

f'(L)>=f'(x)>=f'(l) for every x in [a,b]

i cant understand what is the second law of weirshtass

that gives two extreme points??

there is another things but i got stuck on this

??