I'd check over my work again, according to pg. 39 of this -
http://homepage.smc.edu/geltner_peter/new4to6.pdf
The '1' constant in the numerator shouldn't be negative.
BTW, with that in mind, you end up with 2 + Sqrt(3) as the answer.
[If you don't change the negative sign, you get -2 + sqrt(3)