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Definition

Complex Rational Expression

A complex rational expression is a rational expression in which the numerator, the denominator, or both contain a rational expression. It extends the idea of a complex fraction — where a numerical fraction appears inside another fraction — to algebraic settings where the inner fractions involve variables and polynomials. As with all rational expressions, any variable values that would make any denominator (including inner denominators) equal to zero must be excluded.

Examples of complex rational expressions include:

4y38y29\dfrac{\frac{4}{y-3}}{\frac{8}{y^2-9}}, 1x+1yxyyx\dfrac{\frac{1}{x}+\frac{1}{y}}{\frac{x}{y}-\frac{y}{x}}, and 2x+64x64x236\dfrac{\frac{2}{x+6}}{\frac{4}{x-6}-\frac{4}{x^2-36}}

These expressions can be simplified using two methods: rewriting the expression as a division problem, or multiplying the numerator and denominator by the LCD of all the rational expressions that appear within it.

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Updated 2026-04-21

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