What would you like to understand?

Two fractions $r_1/s_1$ and $r_2/s_2$ are equal in the localization $S^{-1}R$ exactly when there exists an element $t \in S$ such that $t(r_1s_2 - s_1r_2) = 0$. This refines the naive cross-multiplication rule to handle zero-divisor phenomena in general commutative rings.

Conditions: $R$ is a commutative ring.; $S \subset R$ is multiplicatively closed.; $r_1, r_2 \in R$ and $s_1, s_2 \in S$.

Two fractions $r_1/s_1$ and $r_2/s_2$ are equal in the localization $S^{-1}R$ exactly when there exists an element $t \in S$ such that $t(r_1s_2 - s_1r_2) = 0$. This refines the naive cross-multiplication rule to handle zero-divisor phenomena in general commutative rings.

Conditions: $R$ is a commutative ring.; $S \subset R$ is multiplicatively closed.; $r_1, r_2 \in R$ and $s_1, s_2 \in S$.