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Example

Evaluating 2x+33x5\frac{2x+3}{3x-5} for x=0x = 0, x=2x = 2, and x=3x = -3

Evaluate the rational expression 2x+33x5\frac{2x+3}{3x-5} for three different values of xx by substituting each value and simplifying the numerator and denominator separately.

ⓐ When x=0x = 0: Replace xx with 00 to get 2(0)+33(0)5\frac{2(0)+3}{3(0)-5}. Simplify the numerator: 2(0)+3=0+3=32(0)+3 = 0+3 = 3. Simplify the denominator: 3(0)5=05=53(0)-5 = 0-5 = -5. The result is 35=35\frac{3}{-5} = -\frac{3}{5}.

ⓑ When x=2x = 2: Replace xx with 22 to get 2(2)+33(2)5\frac{2(2)+3}{3(2)-5}. Simplify the numerator: 2(2)+3=4+3=72(2)+3 = 4+3 = 7. Simplify the denominator: 3(2)5=65=13(2)-5 = 6-5 = 1. The result is 71=7\frac{7}{1} = 7.

ⓒ When x=3x = -3: Replace xx with 3-3 to get 2(3)+33(3)5\frac{2(-3)+3}{3(-3)-5}. Simplify the numerator: 2(3)+3=6+3=32(-3)+3 = -6+3 = -3. Simplify the denominator: 3(3)5=95=143(-3)-5 = -9-5 = -14. The result is 314=314\frac{-3}{-14} = \frac{3}{14}.

This example demonstrates that evaluating a rational expression follows the same substitute-and-simplify process used for any algebraic expression. After substitution, the numerator and denominator are each simplified independently before the resulting fraction is reduced. Part (ⓒ) illustrates that when both the numerator and denominator are negative, the negatives cancel, producing a positive result.

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Updated 2026-04-21

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