I will assume that behind this question is a myth that there is such a thing as, for example, "The square root of 2".

In fact for any number #a# (in #RR# or #CC#), if #r# is a square root of #a# then #-r# is also a square root of #a#.

If #a in RR# and #a > 0# then #a# has two real square roots - the positive square root that we represent by the symbols #sqrt(a)# and the negative square root, which is #-sqrt(a)#.

If #a in RR# and #a = 0# then #a# has one (repeated) square root, viz #0#.

If #a in RR# and #a < 0# then #a# has two pure imaginary square roots, #sqrt(-a)*i# and #-sqrt(-a)*i#