-1 - 9 = -10
also your -2x mysteriously turned into +2x
so
(x-1)^2 - 10
write in form y=a(x-h)^2+k
y=x^2-x-9
(x^2-2x)-9
complete the square
(x^2+2x+1-1)-9
(x^2+2x+1)-1-9
(x+1)^2-9
3 answers
y= x^2 -x - 9
y=(x^2 -x + 0.5^2 - 0.5^2) -9 ; we get 0.5 by dividing 1 by 2)
y=(x^2 -x + 0.25) - 0.25 -9
y=(x-0.5)^2 - 9.25
y=(x^2 -x + 0.5^2 - 0.5^2) -9 ; we get 0.5 by dividing 1 by 2)
y=(x^2 -x + 0.25) - 0.25 -9
y=(x-0.5)^2 - 9.25
roro is correct, I misread your question