Question 535714: vertex form y=-x^2+6x+4
i need in vertex form i cant find out how to do it?
Answer by KMST(5328)   (Show Source):
You can put this solution on YOUR website! 
Noticing that 6x is double the product of x and 3, I see the first two terms as part of a square. I add and subtract 9 (the square of 3), and group to get
I know that  and just "completed the square."
That gets me to the equation of the parabola in vertex form:
That form of the equation equation tells you the axis of symmetry of the parabola is 
and the vertex is at (3,13).
To get the vertex form, you could "complete the square" as I did, or you could try to memorize an unwieldy formula handed down by someone who just did the same work with the generic parabola equation 
to come up with the formula for the vertex form:
In your case, your a, b, and c values were:
 ,  , and 
If you substitute a, b and c in the monster formula you get your vertex form.
Admittedly, there is an in-between way:
You could just remember the formula for the axis:  ,
which gives you the x-coordinate for the vertex, calculate the value to know what to subtract from x in the vertex form, and then calculate the y-coordinate for the vertex, which is also the last term of the vertex form, by substituting the x-coordinate for the vertex in the equation for the parabola
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