you complete the square
Vertex form is
[tex]f(x) = (x - h)^2 + k~~~~~~~the~~vertex ~~is~~(h, k)[/tex]
so break it into parts
[tex]f(x) = (x^2 + 6x + ??) + 8 - ??[/tex]
to keep the equation in balance to add and subtract the same value
so value ?? is
[tex]?? = ( \frac{6}{2} )^2 [/tex]
then factor the perfect square
