Concept

Factors vs. Terms in Simplification

When simplifying fractions or rational expressions, only factors — quantities that are multiplied together to form a product — can be divided out (cancelled) from the numerator and denominator. A term — a quantity that is part of a sum or difference — cannot be cancelled.

For example, in 3x(x9)5(x9)\frac{3x(x - 9)}{5(x - 9)}, the binomial (x9)(x - 9) is a common factor of both the numerator and denominator because it is multiplied with other quantities. Since it is a factor of the product, it can be divided out, yielding 3x5\frac{3x}{5}.

However, in x+5x\frac{x + 5}{x}, the xx in the numerator is a term of the sum x+5x + 5, not a factor of a product. It cannot be cancelled. Doing so would be the same error as cancelling the 22's in 2+52\frac{2 + 5}{2}, which would incorrectly give 55 instead of the correct value 72\frac{7}{2}.

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Updated 2026-04-21

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