Question 64705
x^2-4x-12
(x-6)(x+2)
x-6=0
x=6 x intercept
x+2=0
x=-2 x intercept
x=6-2/2=4/2=2
y=2^2-2*4-12
y=4-8-12
y=-16 thus the vertex is(2,-16)

{{{ graph( 300, 200, -15, 15, -20, 15, x^2-4x-12) }}} (graph 300x200 pixels, x from -15 to 15, y from -20 to 15, of function x^2-4x-12). 
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MERRY CHRISTMAS