Question

A parabola opening up or down has vertex (0, -3) and passes through (-8, 5). Write its

equation in vertex form.

Answer 1

`~~~~~~\textit{vertical parabola vertex form} \\\\ y=a(x- h)^2+ k\qquad \begin{cases} \stackrel{vertex}{(h,k)}\\\\ \stackrel{a~is~negative}{op ens~\cap}\qquad \stackrel{a~is~positive}{op ens~\cup} \end{cases} \\\\[-0.35em] ~\dotfill`

`\begin{cases} h=0\\ k=-3\\ \end{cases}\implies y=a(~~x-0~~)^2 + (-3)\hspace{4em}\textit{we also know that} \begin{cases} x=-8\\ y=5 \end{cases} \\\\\\ 5=a(-8-0)^2-3\implies 8=64a\implies \cfrac{8}{64}=a\implies \cfrac{1}{8}=a \\\\[-0.35em] ~\dotfill\\\\ ~\hfill {\Large \begin{array}{llll} y=\cfrac{1}{8}x^2-3 \end{array}} ~\hfill`