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

1 Answer
Jul 6, 2017

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))