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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))#

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