y=-x^2-6x
how do I find the vertex?

Question

y=-x^2-6x
how do I find the vertex?

campbell_st · Answer

the vertex lies on the line of symmetry. 

the line of symmetry is found using

$$x = \frac{-b}{2a}$$

in your question a = -1 and b = -6

so the line of symmetry is 

$$x = \frac{- -6}{2  \times (-1)} = -3$$

this is the x value in the vertex

substitute x = -3 into the equation to find the y=value of the vertex

anonymous · Answer

i came up with 9

helder_edwin · Answer

it easier to complete the square (i don't know if you this expresion, it is a literal translation from spanish), but anyway
$$ y=-x^2-6x $$
$$ y-9=-(x^2+6x+9) $$
$$ y-9=-(x+3)^2 $$
now from this, what is the vertex?

campbell_st · Answer

the vertex is (-3, 9)