Solve by completing the square x^2+6x+3=0

X²+6x + ___ = - 3 + ___

The blank is equal to (b/2) ², which is, in this case, 9. However, I would leave it as (3) ² on the left in order to re-write it.

X²+6x + (3) ²=6

(X+3) ²=6

See how the 3 dropped down?

X-3=±√ (6)

X=3±√ (6)

Note: Whenever you take the square root of something, you must include a ± because, for example, 2² = (-2) ² and you must account for all possible answers.