Question 107515
solve by vertex form :
You do not "solve" by vertex form.  You may "put the equation" 
into vertex form. But that is not "solving" it.
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y = x^2+6x-12
x^2+6x+? = y+12+?
x^2+6x+9 = y+12+9
(x+3)^2 = y+21
Vertex: (-3,-21)
{{{graph(400,300,-10,10,-30,10,x^2+6x-12)}}}
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y = 4x^2-24x-11
4x^2-24x = y+11
4(x^2-6x+?) = y+11+4?
4(x^2-6x+9) = y+11+36
4(x-3)^2 = y+47
(x-3)^2 = (1/4)(y+47)
Vertex: (3,-47)
{{{graph(400,300,-10,10,-50,10,4x^2-24x-11)}}}
Cheers,
Stan H.