Note 1 to entry: Every non-zero real or complex number has two square roots, each being the negative of the other. For a non-negative real number a, the non-negative square root is denoted by $a^{1/2}$ or $\sqrt{a}$. For a negative real number a, the number $-a$ is positive and the two square roots are imaginary numbers, conjugate of each others, denoted by $j\sqrt{-a}$ and $-j\sqrt{-a}$. For a complex number $c=\left|c\right|e^{j\phi }$, the two square roots are $\sqrt{\left|c\right|}{e}^{j\phi /2}$ and $\sqrt{\left|c\right|}{e}^{j(\frac{\phi }{2}+\pi )}$.

Note 2 to entry: The concept of square root may be applied to scalar quantities.