How do you find the intercept and vertex of #y=(-x-1)(x+7)#?

1 Answer
Nallasivam V
Feb 12, 2018

X-intercepts

#(-1, 0)#
#(-7, 0)#
Y- intercept
#(0, -7)#
Vertex
#(-4. 9)#

Explanation:

#y=(-x-1)(x+7)#
#y=-x^2-x-7x-7#
#y=-x^2-8x-7#
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X-intercepts
At #y=0#
#(-x-1)(x+7)=0#
#-x-1=0#
#-x=1#
#x=-1#
#(1, 0)#
#x+7=0#
#x=-7#
#(-7, 0)#

Y- intercept
At #x=0#

#y=(0-1)(0+7)#
#y=-7#
#(0, -7)#

Vertex

#y=-x^2-8x-7#
#x=(-b)/(2a)=8/(-2)=-4#
At #x=-4#
#y=-(-4)^2-8(-4)-7#
#y=-16+32-7=-23+32=9#
#(-4. 9)#

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