Thanks MathCuber 
Attn: asker
this is a good concept for you to work out quickly.
\(\sqrt{169}=+13\qquad \text{(never -13, this is by convention)}\\ \)
However if
\(y^2=169\)
then it is you that must introduce the square root sign,
which means that both the negative and the positive are answer.
\(y^2=169\\ y=\pm\sqrt169\\ y=+13\;\;\;\;or\;\;\;\;y=-13\)
.