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One-sided limits and existence of a two-sided limit

Consider the function h2(x)={∣x−3∣x−3+1x≠35x=3h_2(x) = \begin{cases} \dfrac{|x-3|}{x-3} + 1 & x \neq 3 \\ 5 & x = 3 \end{cases}

Consider the function h2(x)h_2(x) defined above. Investigate the behavior of h2(x)h_2(x) for xx near 33, both from the left and from the right, using the graph below as a guide.

One-sided limits and existence of a two-sided limit graph

Does lim⁡x→3h2(x)\displaystyle\lim_{x \to 3} h_2(x) exist? If it exists, give its value; if it does not exist, explain which of the standard reasons applies.

Hint

Compute or estimate the left-hand limit lim⁡x→3−h2(x)\lim_{x\to 3^-} h_2(x) and the right-hand limit lim⁡x→3+h2(x)\lim_{x\to 3^+} h_2(x) separately using the definition of ∣x−3∣|x-3| on each side. Remember that the value h2(3)=5h_2(3) = 5 is irrelevant to the limit.

Step-by-step solution

For x<3x < 3, we have x−3<0x - 3 < 0, so ∣x−3∣=−(x−3)|x-3| = -(x-3), giving ∣x−3∣x−3=−1\dfrac{|x-3|}{x-3} = -1. Thus h2(x)=−1+1=0h_2(x) = -1 + 1 = 0 for all xx near 33 from the left, so lim⁡x→3−h2(x)=0\lim_{x\to 3^-} h_2(x) = 0.

For x>3x > 3, we have x−3>0x - 3 > 0, so ∣x−3∣=x−3|x-3| = x-3, giving ∣x−3∣x−3=1\dfrac{|x-3|}{x-3} = 1. Thus h2(x)=1+1=2h_2(x) = 1 + 1 = 2 for all xx near 33 from the right, so lim⁡x→3+h2(x)=2\lim_{x\to 3^+} h_2(x) = 2.

Since the left-hand limit (00) and the right-hand limit (22) are not equal, the two-sided limit lim⁡x→3h2(x)\lim_{x\to 3} h_2(x) does not exist. Note that the value h2(3)=5h_2(3) = 5 plays no role in this conclusion, since limits depend only on behavior near x=3x=3, not at x=3x=3.

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