the question:

there is a function f(x) which is continues in the borders [a,b]
and derivitable in the borders (a,b), b>a>0
alpha differs 0
prove the there is b>c>a

in that formula:
http://img392.imageshack.us/my.php?i...1208753je3.gif

my trial:

http://img149.imageshack.us/img149/4647/img9136sg3.gif

i dont know what the purpose of this question
what doi need to do next??

I think this is a problem on the mean value theorem? In which case, I think you have to show that there is a point a<c<b where the tangent to the curve is parallel to the line drawn between and .