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Behavior near a vertical asymptote

Consider the function f(x)=2x2−5x−3x2−9f(x) = \dfrac{2x^2 - 5x - 3}{x^2 - 9}

Identifying a removable discontinuity

Factor the numerator and denominator of f(x)=2x2−5x−3x2−9f(x) = \dfrac{2x^2 - 5x - 3}{x^2 - 9} to determine the behavior as x→3x \to 3. Note that x=3x = 3 is a zero of the denominator. Check whether x=3x = 3 is also a zero of the numerator. After factoring completely, determine lim⁡x→3f(x)\lim_{x \to 3} f(x). Your answer should be +∞+\infty, −∞-\infty, a finite value, or a statement that the two-sided limit does not exist because the one-sided limits disagree in sign.

Hint

Factor 2x2−5x−32x^2 - 5x - 3 and x2−9x^2 - 9 completely. Check whether the factor (x−3)(x-3) appears in both the numerator and denominator. If it cancels, you have a removable discontinuity. If it doesn't cancel from the denominator, you have a vertical asymptote.

Step-by-step solution

Factor both polynomials: 2x2−5x−3=(2x+1)(x−3)2x^2 - 5x - 3 = (2x+1)(x-3) and x2−9=(x−3)(x+3)x^2 - 9 = (x-3)(x+3). Canceling the common factor (x−3)(x-3) (valid since x≠3x \ne 3) gives f(x)=2x+1x+3f(x) = \dfrac{2x+1}{x+3} for x≠3x \neq 3. This simplified form reveals that near x=3x=3, the numerator 2x+12x+1 approaches 77 while the denominator x+3x+3 approaches 66, both nonzero.

Since 2x+1x+3→76\dfrac{2x+1}{x+3} \to \dfrac{7}{6} as x→3x \to 3, and this is a finite nonzero value, the original limit is actually finite, not infinite. Evaluating directly: lim⁡x→3f(x)=2(3)+13+3=76\lim_{x\to 3} f(x) = \dfrac{2(3)+1}{3+3} = \dfrac{7}{6}. Because the factor causing the zero denominator canceled, x=3x=3 is a removable discontinuity (a hole), not a vertical asymptote, so the limit exists and equals 76\dfrac{7}{6}.

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