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Left-hand limit from a table of values

Consider the piecewise function h(x)={x2x<12x−1x≥1h(x) = \begin{cases} x^2 & x < 1 \\ 2x - 1 & x \ge 1 \end{cases} We want to investigate the behavior of h(x)h(x) as xx approaches 11.

Build a table of values of h(x)h(x) for x=0.9,0.99,0.999,0.9999x = 0.9, 0.99, 0.999, 0.9999 (values approaching 11 from the left, using the rule x2x^2 since these values are less than 11). Based on the trend in your table, what value does h(x)h(x) appear to approach as x→1−x \to 1^-? That is, estimate lim⁡x→1−h(x).\lim_{x \to 1^-} h(x).

Hint

Since each of these xx-values is less than 1, use the rule h(x)=x2h(x) = x^2 to compute the outputs, then observe what value they seem to be getting closer to.

Step-by-step solution

For xx slightly less than 11, we use the branch h(x)=x2h(x) = x^2. Computing values: h(0.9)=0.81h(0.9) = 0.81, h(0.99)=0.9801h(0.99) = 0.9801, h(0.999)=0.998001h(0.999) = 0.998001, and h(0.9999)=0.99980001h(0.9999) = 0.99980001. These outputs are clearly getting closer and closer to 11 as xx gets closer to 11 from below.

Since the outputs approach 11 as xx approaches 11 from the left, we conclude lim⁡x→1−h(x)=1\lim_{x \to 1^-} h(x) = 1. Note this is true even though h(1)h(1) itself is computed using the other branch — the limit only depends on values near 11, not at 11.

Right-hand limit from a table of values

Now build a table of values of h(x)h(x) for x=1.1,1.01,1.001,1.0001x = 1.1, 1.01, 1.001, 1.0001 (values approaching 11 from the right, using the rule 2x−12x-1 since these values are at least 11). Based on the trend in your table, estimate lim⁡x→1+h(x).\lim_{x \to 1^+} h(x).

Hint

For these xx-values, x≥1x \ge 1, so use the rule h(x)=2x−1h(x) = 2x - 1 to compute the outputs, then see what value they approach.

Step-by-step solution

For xx slightly greater than 11, we use the branch h(x)=2x−1h(x) = 2x - 1. Computing values: h(1.1)=1.2h(1.1) = 1.2, h(1.01)=1.02h(1.01) = 1.02, h(1.001)=1.002h(1.001) = 1.002, and h(1.0001)=1.0002h(1.0001) = 1.0002. These outputs steadily decrease toward 11 as xx approaches 11 from above.

Since the outputs approach 11 as x→1+x \to 1^+, we conclude lim⁡x→1+h(x)=1\lim_{x \to 1^+} h(x) = 1.

Existence of the two-sided limit

Using your conclusions from the left-hand and right-hand limits, does lim⁡x→1h(x)\lim_{x \to 1} h(x) exist? If it exists, state its value.

Hint

Recall that a two-sided limit exists exactly when both one-sided limits exist and agree with each other.

Step-by-step solution

From part (a), lim⁡x→1−h(x)=1\lim_{x \to 1^-} h(x) = 1, and from part (b), lim⁡x→1+h(x)=1\lim_{x \to 1^+} h(x) = 1. Since both one-sided limits exist and are equal to the same value, the two-sided limit exists.

Therefore lim⁡x→1h(x)=1\lim_{x \to 1} h(x) = 1. Note that this value happens to match h(1)=2(1)−1=1h(1) = 2(1)-1 = 1 as well, but that agreement is not required for the limit to exist — only the one-sided limits needed to match each other.

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