[tex]\bf \textit{vertex of a vertical parabola, using coefficients} \\\\ f(x)=\stackrel{\stackrel{a}{\downarrow }}{-2}x^2\stackrel{\stackrel{b}{\downarrow }}{+8}x\stackrel{\stackrel{c}{\downarrow }}{-11} \qquad \qquad \left(-\cfrac{ b}{2 a}~~~~ ,~~~~ c-\cfrac{ b^2}{4 a}\right) \\\\\\ \left( -\cfrac{8}{2(-2)}~~,~~-11-\cfrac{8^2}{4(-2)} \right)\implies \left( 2~~,~~-11+\cfrac{64}{8} \right) \\\\\\ (2~~,~~-11+8)\implies (2~~,~~-3)[/tex]
