\displaystyle NEG1S \frac{A}{B} \times NEG2S \frac{C}{D}
\displaystyle {} = \frac{NEG1 * A \times NEG2 * C}{B \times D}
\displaystyle {} = \frac{NEG1 * A * NEG2 * C}{B * D}
\displaystyle {} = fractionReduce(NEG1 * A * NEG2 * C, B * D)