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.