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One-sided limits and existence of a two-sided limit at a piecewise boundary

Consider the piecewise function g(x)={3x+1x<2x2x≥2g(x) = \begin{cases} 3x+1 & x < 2 \\ x^2 & x \ge 2 \end{cases}

Using the definition of g(x)g(x) above, evaluate the left-hand limit lim⁡x→2−g(x)\lim_{x\to 2^-} g(x) and the right-hand limit lim⁡x→2+g(x)\lim_{x\to 2^+} g(x). Based on these results, does lim⁡x→2g(x)\lim_{x\to 2} g(x) exist? If it exists, state its value; if it does not, explain why not.

Hint

Remember that for xx near 2 but less than 2, you must use the formula 3x+13x+1, and for xx near 2 but greater than or equal to 2, you must use x2x^2. Evaluate each piece as xx approaches 2 from its respective side.

Step-by-step solution

For the left-hand limit, since x<2x < 2, we use g(x)=3x+1g(x) = 3x+1. As x→2−x \to 2^-, this expression approaches 3(2)+1=73(2)+1 = 7, so lim⁡x→2−g(x)=7\lim_{x\to 2^-} g(x) = 7.

For the right-hand limit, since x≥2x \ge 2, we use g(x)=x2g(x) = x^2. As x→2+x \to 2^+, this expression approaches 22=42^2 = 4, so lim⁡x→2+g(x)=4\lim_{x\to 2^+} g(x) = 4.

Since the left-hand limit (7) and the right-hand limit (4) are not equal, the two-sided limit lim⁡x→2g(x)\lim_{x\to 2} g(x) does not exist. This is a case where the one-sided limits disagree, so the function does not settle to a single value as xx approaches 2.

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