Question

A parabola has its turning point at x=4 and one of the x-intercepts is x=−3.

What is the x value of the other x-intercept?

Answer 1

a(x-4)^2 + k = a(x+3)(x-m)
ax^2 - 8ax + 16a+k = ax^2 + a(3-m)x - 3am
m = 11
So the other root is -11

Answer 2

Oops -- a typo.
m = 11, not -11

Another way is --
Let the other root be m
Since the sum of the roots is -b/a
and we know that -b/2a = 4, we have -b/a = 8
8 = -3 + m
m = 11

Answer 3

Just realized that all that math was unnecessary. The vertex is midway between the roots.
-3 = 4-7
So the other root is at 4+7 = 11