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Checking the three-part continuity test at x = 2

Consider the function f(x)={x2−4x−2x≠23x=2f(x) = \begin{cases} \dfrac{x^2-4}{x-2} & x \neq 2 \\ 3 & x = 2 \end{cases}

Determine whether f(x)f(x) is continuous at x=2x=2. To justify your answer, check each of the three conditions required for continuity at a point: (1) is f(2)f(2) defined, (2) does lim⁡x→2f(x)\lim_{x \to 2} f(x) exist, and (3) does that limit equal f(2)f(2)? Based on your findings, state whether ff is continuous at x=2x=2, and if not, classify the discontinuity as removable, jump, or infinite.

Hint

Factor x2−4x^2-4 as (x−2)(x+2)(x-2)(x+2) to simplify the fraction for x≠2x \neq 2, then use this simplified form to evaluate the limit as x→2x \to 2. Compare that limit value to the given value f(2)=3f(2)=3.

Step-by-step solution

First check condition 1: f(2)f(2) is given directly in the definition as f(2)=3f(2) = 3, so this value is defined. Next, for x≠2x \neq 2, simplify f(x)=x2−4x−2=(x−2)(x+2)x−2=x+2f(x) = \dfrac{x^2-4}{x-2} = \dfrac{(x-2)(x+2)}{x-2} = x+2, since x−2≠0x-2 \neq 0 allows cancellation. This simplification lets us compute the limit using a polynomial expression instead of the original rational expression.

Now check condition 2: lim⁡x→2f(x)=lim⁡x→2(x+2)=4\lim_{x\to 2} f(x) = \lim_{x \to 2}(x+2) = 4, so the limit exists and equals 44. Finally check condition 3: compare the limit value 44 to f(2)=3f(2) = 3 — they are not equal, so condition 3 fails. Therefore ff is not continuous at x=2x=2. Since the limit exists but does not equal f(2)f(2), this is a removable discontinuity.

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