Example

Finding Undefined Values of 8a2b3c\frac{8a^2b}{3c}, 4b32b+5\frac{4b-3}{2b+5}, and x+4x2+5x+6\frac{x+4}{x^2+5x+6}

To determine the values for which each rational expression is undefined, set the denominator equal to zero and solve for the variable.

8a2b3c\frac{8a^2b}{3c}: The denominator is 3c3c. Setting it equal to zero gives 3c=03c = 0, which yields c=0c = 0. Thus, the expression is undefined for c=0c = 0.

4b32b+5\frac{4b - 3}{2b + 5}: The denominator is 2b+52b + 5. Set it equal to zero and solve: 2b+5=02b + 5 = 0 2b=52b = -5 b=52b = -\frac{5}{2} Thus, the expression is undefined for b=52b = -\frac{5}{2}.

x+4x2+5x+6\frac{x + 4}{x^2 + 5x + 6}: The denominator is x2+5x+6x^2 + 5x + 6. Set it equal to zero and factor: x2+5x+6=0x^2 + 5x + 6 = 0 (x+2)(x+3)=0(x + 2)(x + 3) = 0 x+2=0 or x+3=0x + 2 = 0 \text{ or } x + 3 = 0 x=2 or x=3x = -2 \text{ or } x = -3 Thus, the expression is undefined for x=2x = -2 or x=3x = -3.

These examples show increasing complexity: a monomial denominator yields a single restricted value directly, a binomial denominator requires solving a two-step linear equation, and a quadratic trinomial denominator requires factoring and applying the Zero Product Property.

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Updated 2026-05-14

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