How do you complete the square for :x2+6x?

1 Answer
George C.
May 16, 2015

(x+3)2=x2+6x+9

So x2+6x=(x+3)2−9

If you were actually trying to solve x2+6x=0, then completing the square would be a round about way of doing it, but would look something like this:

0=x2+6x=x2+6x+9−9=(x+3)2−9

Adding 9 to both sides you get (x+3)2=9

So x+3=±√9=±3

Then subtracting 3 from both sides, you get

x=−3±3

In other words x=0 or x=−6.

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