Question

A parabola intersects the x-axis at x=3 and x=9 what is the x-coordinate of the parabola's vertex?

Answer 1

Here we are given the x intercepts at x=3 and x=9

So let us try to make quadratic equation for this using given information.

We have factors in the form (x-a)(x-b)

where a and b are x intercepts given to us.

So rewriting in factored form:

$y=(x-3)(x-9)$

Now let us simplify it:

$y=x^{2}-12x+27$

Let us find the vertex now,

For a quadratic equation of the form:

$y=ax^{2}+bx+c$

For x coordinate , we have the formula,

$x=\frac{-b}{2a}$

So using this formula for our equation,

$x=\frac{-(-12)}{2(1)}$

So x = 6

Answer: The x-coordinate of the parabola's vertex is 6.

Answer 2

Plug in the numbers into demos. You can pretty much use this for any parabola equation.
https://www.desmos.com/calculator<span />