Calculus · real student question

Evaluate the limit of (2x^2 + x - 3)/|x - 1| as x approaches -2.

Question

Evaluate

limx22x2+x3x1.\lim_{x\to-2}\frac{2x^{2}+x-3}{|x-1|}.

Step-by-step solution

  1. Check the denominator before doing anything clever. Absolute-value denominators usually signal a one-sided analysis, but only when the expression inside can vanish at the limit point. Here

    x1 is zero only at x=1,|x-1|\ \text{is zero only at}\ x=1,

    and the limit point is x=2x=-2, comfortably away from it. So there is no indeterminate form to resolve.

  2. Resolve the absolute value on a neighbourhood of x=2x=-2. For xx near 2-2 we have x1<0x-1<0 (at x=2x=-2 it equals 3-3), so on that whole neighbourhood

    x1=(x1)=1x.|x-1|=-(x-1)=1-x.

    Rewriting removes the absolute value entirely and shows the function is a ratio of two polynomials near x=2x=-2 — hence continuous there.

  3. Confirm the form is not 0/0. Evaluating numerator and denominator separately at x=2x=-2:

    2(2)2+(2)3=823=3,21=3=3.2(-2)^{2}+(-2)-3=8-2-3=3,\qquad |-2-1|=|-3|=3.

    Both are nonzero, so no factoring, rationalising, or L'Hopital step is needed — those tools exist for indeterminate forms only.

  4. Apply direct substitution. Since the function is continuous at x=2x=-2, the limit is just the function value:

    limx22x2+x3x1=33=1.\lim_{x\to-2}\frac{2x^{2}+x-3}{|x-1|}=\frac{3}{3}=1.

  5. Confirm the two one-sided limits agree. Approaching from the left (x=2.001x=-2.001): 2(4.004)+(2.001)33.001=3.0073.0011.002\frac{2(4.004)+(-2.001)-3}{3.001}=\frac{3.007}{3.001}\approx 1.002. From the right (x=1.999x=-1.999): 2.9932.9990.9980\frac{2.993}{2.999}\approx 0.9980. Both tend to 11 as the step shrinks, so the two-sided limit exists and equals 11 ✓. Contrast this with limx12x2+x3x1\lim_{x\to1}\frac{2x^{2}+x-3}{|x-1|}, where the absolute value really does force different left and right values.

Answer

limx22x2+x3x1=33=1\lim_{x\to-2}\frac{2x^{2}+x-3}{|x-1|}=\frac{3}{3}=1

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