Question 63988
{{{h(x) = sqrt(x^2-6x+8)}}}
{{{h(x) = sqrt((x-2)(x-4))}}}
Only the positive square root is indicated, so h(x)
can never be negative.
That means the range of h(x) is 0 < h < plus infinity 
The values that make h(x) = 0 are the roots, x = 2 and x = 4
Any values of x that make (x-2)(x-4) negative result in
the square root of a negative number and cannot be plotted
(x-2)(x-4) is negative when 2 < x < 4 
So, the domain of h is 2 > x > 4
The plot looks like a parabola with everything below the x-axis 
missing.