Posted by **Brian** on Sunday, December 17, 2006 at 6:51pm.

Find the critical number(s) of f(x)= abs(2x-4)

What is the derivative of abs(2x-4)?

Is it abs(2)?

No. You have to specify the domain of x. At x=2, this function has no derivative.

At x>2, f' = d (2x -4)/dx= 2

at x <2, f'= d(4-2x)/dx= -2

You have to watch for discontinuities on abs functions.