A function f[x] and a point x=a. If f'[a]>0, is it possible f[a]<=f[x]

[CAG]

You've got a function f[x] and a point x=a.
If f'[a]>0, is it possible that f[a]<=f[x] a for all other x's?
Why?

Having a problems visualize this, any help would be great

 

[Poncho]

If f'[a] is positive, the function is increasing at a. For f[a]<=f[x] to be true, "a" needs to be a maxima.

 

[amcavoy]

If f'[a] is positive, the function is increasing at a. For f[a]<=f[x] to be true, "a" needs to be a maxima.

Do you mean minima?

...and by the way, if it was a minima, f'(a) would be 0. So since f'(a)>0, what does that tell you about x<a?

 

[cefarix]

I good example would be f(x) = \sin x the derivative of which is f&#039;(x) = \cos x. If a = 0 then f&#039;(0) = \cos 0 = 1 indicating the function is rising. However, since sine is a repeating function, it will go to a maximum of 1, and fall down again. So f(a) <= f(x) for all x > a is not true if f(x) repeats on the segment a < x < inf.