Then why do we always use the pluss/minus sign in solutions to second order equations?

Edit: Okey, I looked up the definition of square root and saw it could be both the values. According to wikipedia, there is the principal square root, apperantly, and the other square root.

Another thing I didn't quite understand was if the $\displaystyle \sqrt{\ } $ symbol denoted the principal square root or not. First it says it does, then it says that "The square root symbol ($\displaystyle \sqrt{\ }$) was first used during the 16th century".