Question

What is the vertex of `y=-x^2 - 18x + 9`?

Answer 1

`y=-x^2-18x+9`

Factor out the coefficient of the highest power of `x` (`a` value):
`y=-[x^2+18x-9]`

Rewrite what's inside the brackets using vertex form
`y=-[(x+9)^2-81+9]`

`y=-[(x+9)^2-72]`

Finally distribute the negative sign throughout the brackets
`y=-(x+9)^2+72`

`color(blue)("The vertex of the parabola is at "(-9,72))`