How do I use the vertex formula to determine the vertex of the graph for $f(x)= -x^2-6x$ ?

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Answer 1 · 2015-05-08T19:35:17

You know the graph of that function is a parabola with vertical axis of symmetry, because it's:

$y=ax^2+bx+c$ , with $a=-1, b=-6 and c=0$ ,

so you can use the vertex formula

$x_v=-b/2a=-(-6)/(-2)=-3$
$y_v=f(x_v)=-(-3)^2-6*(-3)=-9+18=9$

so $v=(-3,9)$

How do I use the vertex formula to determine the vertex of the graph for f(x)= -x^2-6xf(x)= -x^2-6x?