Given f(x), to find f(x-3), you have to plug in (x-3) to everywhere you see (x) in the original function.
f(x - 3) = [(x - 3)^2 - 9]^(1/2)
Notice how I replaced the x with x - 3. Now just simplify the function.
f(x - 3) = (x^2 - 6x + 9 - 9)^(1/2)
= sqrt(x^2 - 6x)
****(Anything to the power of (1/2) is the same thing as taking the square root of it.)
