[tex]\bf y=a(x-\boxed{h})^2+\boxed{k}\qquad vertex\ (h,k)
\\ \quad \\
\textit{we know the vertex is at 4,-3}\implies
\begin{array}{lrlll}
4&-3\\
h&k
\end{array}
\\ \quad \\
y=a(x-h)^2+k\\\\ y=a(x-(4))^2+(-3)\implies y=a(x-4)^2-3
\\ \quad \\
\textit{we also know that}
\begin{cases}
x=5\\
y=-6
\end{cases}\textit{ so, what is the coefficient "a"?}
\\ \quad \\
\boxed{-6}=a(\boxed{5}-4)^2-3\impliedby \textit{solve for "a"}[/tex]
