How do I plug 3+/- √9 into these equations?

Question

y= -x²+9x-3 and the line y=3x
I got the anwser 3+/- √9, but how do I apply this to the equations?

Show/explain please.

Answer 1

How did you get this answer?
y = 3x = -x²+9x-3 therefore x² - 6x + 3 = 0
x = [6+-√(36 - 12)]/2 = 3+-√6