Question 1024230
You don't even have to use formulas to find the vertex of the parabola if you know the roots.

y = (x-4)(x+2) ==> the roots of the equation are 4 and -2.  The x-coordinate of the vertex should be the average of the two roots, namely {{{(4+(-2))/2 = 1}}}.  To find the y-coordinate of the vertex plug it into the original equation:
y = (1-4)(1+2) = -3*3 = -9.
==> (h,k) = (1,-9)


==> {{{y = x^2 - 2x - 8}}}, the standard form of the equation