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Opposites in a Rational Expression

When the numerator and denominator of a rational expression are opposites of each other — meaning one is the negative of the other — the expression simplifies to 1-1. Specifically, the opposite of aba - b is bab - a, and their ratio satisfies:

abba=1ab\frac{a - b}{b - a} = -1 \qquad a \neq b

This result follows from the algebraic identity ba=(ab)b - a = -(a - b): substituting into the fraction gives ab(ab)=1\frac{a - b}{-(a - b)} = -1. An expression and its opposite always divide to 1-1. Recognizing opposite factors in the numerator and denominator of a rational expression is a key simplification technique — when such factors are divided, they produce 1-1 rather than canceling to 11.

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Updated 2026-05-01

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