Question

Write the equation of the parabola in vertex form.

vertex (3,1), point (2,-5)

f(x) = ___

Answer 1

just a quick addition to the superb reply by "reinhard10158" above

`~~~~~~\textit{vertical parabola vertex form} \\\\ y=a(x- h)^2+ k\qquad \begin{cases} \stackrel{vertex}{(h,k)}\\\\ \stackrel{`

`\begin{cases} h=3\\ k=1 \end{cases}\implies y=a(x-3)^2 + 1\hspace{5em}\textit{we also know that} \begin{cases} x=2\\ y=-5 \end{cases} \\\\\\ -5=a(2-3)^2 + 1\implies -6=a(-1)^2\implies -6=a \\\\[-0.35em] ~\dotfill\\\\ ~\hfill {\Large \begin{array}{llll} y=-6(x-3)^2 + 1 \end{array}} ~\hfill`

Answer 2

Explanation:

vertex form :

y = a(x - h)² + k

(h, k) are the coordinates of the vertex.

"a" is the orientation (up-down) and widening factor.

we use the given h, k and x, y (the given point) to calculate "a".

-5 = a(2 - 3)² + 1 = a(-1)² + 1 = a + 1

a = -6

and the full vertex form is then

y = -6(x - 3)² + 1