Question

What is the axis of symmetry of f(x) = -2x2 + 8x - 7

Answer 1

bearing in mind that the squared variable is the "x", and thus this is a vertical parabola, therefore its axis of symmetry will come from the x-coordinate of its vertex.

`\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 }}{-7} \qquad \qquad \left(-\cfrac{ b}{2 a}~~~~ ,~~~~ c-\cfrac{ b^2}{4 a}\right) \\\\\\ \left(-\cfrac{8}{2(-2)}~,~-7-\cfrac{8^2}{4(-2)} \right)\implies \left( \cfrac{8}{4}~,~-7+8 \right)\implies (2,1) \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ ~\hfill \stackrel{\textit{axis of symmetry}}{x=2}~\hfill`