take 1/2 of linear coefient (-6), so 1/2 of -6 is -3
square it ( (-3)^2=9)
add that to both sides
[tex]x^2-6x+9=7+9[/tex]
[tex]x^2-6x+9=16[/tex]
factor perfect square trinomial
[tex](x-3)^2=16[/tex]
sqrt both sides, remember to take positive and negative roots
x-3=+/-4
add 3
x=3+/-4
x=-1 or 7
