Calculus · real student question

Evaluate the limit of (4 - x^2)/(2x^2 + x^3) as x approaches -2.

Question

Evaluate

limx24x22x2+x3\lim_{x\to -2}\frac{4-x^2}{2x^2+x^3}

Step-by-step solution

  1. Test substitution. At x=2x=-2 the numerator is 44=04-4=0 and the denominator is 88=08-8=0, so the form is 00\frac{0}{0} and a shared factor must be present.

  2. Factor the numerator. As a difference of squares, 4x2=(2x)(2+x)4-x^2=(2-x)(2+x). Note the order: writing it as (x2)(x+2)-(x-2)(x+2) is equivalent but easier to get a sign wrong with.

  3. Factor the denominator. Pull out the common x2x^2: 2x2+x3=x2(2+x)2x^2+x^3=x^2(2+x).

  4. Cancel the common factor. For x2x\neq -2 the quotient equals (2x)(2+x)x2(2+x)=2xx2\frac{(2-x)(2+x)}{x^2(2+x)}=\frac{2-x}{x^2}, and the point x=2x=-2 itself is irrelevant to the limit.

  5. Substitute into the reduced form. 2(2)(2)2=44=1\frac{2-(-2)}{(-2)^2}=\frac{4}{4}=1.

  6. Interpret the result. The original function has a removable discontinuity at x=2x=-2: filling in the value 11 would make it continuous there.

Answer

11

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