Nice catch.... yes, a typo should be -a^2 and yes... should have used the square root instead of factoring the entire thing out (tedious). Correct?
so...
Just a quick check if someone wouldn't mind (different problem):
thanks!
as for completing the square... still trying to burn that into my brain with no luck.
The completing the square idea works according to
To work backwards from that, you examine the multiplier of x and take half of it...
x is multiplied by 2b, so half of that is b, hence we need to introduce by adding to both sides
Now the left side is a "multiplied out" square
so you can continue by taking the square root of both sides as before