for all x, x*
i know that for the function to be concave all the points on the tangent need to be on or below the function...but i doesn't help...i've been staring at the problems for days now, with no result...
Homework Statement
f:R->R, c'
prove that f is concave iff f(x*)+(x-x*)f'(x*)>=f(x)
Homework Equations
assume the function is only once differentiable
The Attempt at a Solution
i have no idea how to approach this question...:confused: