Definitions:
1.
A number
a in the domain of a given function f is called a critical number of f if f
'(a) = 0 or f ' is undefined at x = a.
2.
Relative
extrema are the minimums or maximum points on a part of a curve, while absolute
extrema are the minimums and maximum points along the entire curve.
Now we are
looking at the following curve:
f (x) =
To find the
extrema, we take the first derivative and figure out at what value of x, the
first derivate of the function equals to zero:
f’(x) = 2x-6
f’(3) = 0
As you can see
the function is decreasing from negative infinity to 3, and increasing from 3
to infinity. The critical number is 3. There is only one relative (or local)
minimum at (3, -9).