Answer:
The square root function
sqrt(144) or √144 produces a single positive value, 12.
However if you have an equation
x² = 144, then you have two possible values for x, 12 and -12.
Two ways to look at it.
x² - 144 = 0
Difference of two squares
(x+12)(x-12) = 0
x = -12, 12
x² = 144
x = ±√144
x = ±12
x = -12, 12