Square class
= Square class
{title2=$[a]\in K^*/K^{*2}$}
The square class of $a\in K^*$ is its image in the <square-class group of a field> $K^*/K^{*2}$. Two nonzero elements have the same square class exactly when their quotient is a square. Every element of this quotient has order dividing $2$. Over the <rational numbers>, a square class has a unique signed squarefree integer representative.