Question

What is the location of the vertex of the parabola defined by f(x) = −x2 + 8x − 21 and in what direction does the parabola open?

Answer 1

`\bf \qquad \qquad \textit{vertex of a parabola}\\ \quad \\ \begin{array}{llllll} f(x)&=&-1x^2&+8x&-21\\ &&\uparrow &\uparrow &\uparrow \\ &&a&b&c \end{array}\qquad \left(-\cfrac{{{ b}}}{2{{ a}}}\quad ,\quad {{ c}}-\cfrac{{{ b}}^2}{4{{ a}}}\right)`

the squared variable is the "x", thus is going vertical, down or up? well
the leading term's coefficient is negative, that means, down