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Right-hand limit of f(x) as x approaches -1

Consider the function f(x)=∣x+1∣x+1f(x) = \dfrac{|x+1|}{x+1}. We want to investigate the behavior of f(x)f(x) as xx approaches −1-1.

Evaluate f(x)=∣x+1∣x+1f(x) = \dfrac{|x+1|}{x+1} for values of xx slightly greater than −1-1 (such as x=−0.9,−0.99,−0.999x = -0.9, -0.99, -0.999) to build a table of values. Based on this trend, what is lim⁡x→−1+f(x)\displaystyle\lim_{x \to -1^+} f(x)?

Hint

For x>−1x > -1, the quantity x+1x+1 is positive, so ∣x+1∣=x+1|x+1| = x+1. Simplify f(x)f(x) under this assumption before plugging in values close to −1-1.

Step-by-step solution

When x>−1x > -1, we have x+1>0x + 1 > 0, so ∣x+1∣=x+1|x+1| = x+1. Substituting into f(x)f(x) gives f(x)=x+1x+1=1f(x) = \dfrac{x+1}{x+1} = 1 for all such xx.

Since f(x)f(x) equals the constant value 11 for every xx slightly greater than −1-1, the values in the table stay fixed at 11 and do not change as x→−1+x \to -1^+. Therefore lim⁡x→−1+f(x)=1\displaystyle\lim_{x \to -1^+} f(x) = 1.

Left-hand limit of f(x) as x approaches -1

Now evaluate f(x)=∣x+1∣x+1f(x) = \dfrac{|x+1|}{x+1} for values of xx slightly less than −1-1 (such as x=−1.1,−1.01,−1.001x = -1.1, -1.01, -1.001) to build a table of values. Based on this trend, what is lim⁡x→−1−f(x)\displaystyle\lim_{x \to -1^-} f(x)?

Hint

For x<−1x < -1, the quantity x+1x+1 is negative, so ∣x+1∣=−(x+1)|x+1| = -(x+1). Simplify f(x)f(x) under this assumption before plugging in values close to −1-1.

Step-by-step solution

When x<−1x < -1, we have x+1<0x + 1 < 0, so ∣x+1∣=−(x+1)|x+1| = -(x+1). Substituting into f(x)f(x) gives f(x)=−(x+1)x+1=−1f(x) = \dfrac{-(x+1)}{x+1} = -1 for all such xx.

Since f(x)f(x) equals the constant value −1-1 for every xx slightly less than −1-1, the values in the table stay fixed at −1-1 as x→−1−x \to -1^-. Therefore lim⁡x→−1−f(x)=−1\displaystyle\lim_{x \to -1^-} f(x) = -1.

Existence of the two-sided limit

Using your results for the one-sided limits from parts (a) and (b), does lim⁡x→−1f(x)\displaystyle\lim_{x \to -1} f(x) exist? Justify your conclusion.

Hint

Recall that a two-sided limit exists only when both one-sided limits exist and are equal to each other.

Step-by-step solution

From part (a), lim⁡x→−1+f(x)=1\displaystyle\lim_{x \to -1^+} f(x) = 1, and from part (b), lim⁡x→−1−f(x)=−1\displaystyle\lim_{x \to -1^-} f(x) = -1.

Since the left-hand limit and right-hand limit are not equal (−1≠1-1 \neq 1), the two-sided limit lim⁡x→−1f(x)\displaystyle\lim_{x \to -1} f(x) does not exist.

Sign of the constant value approached from the right

Hint
Step-by-step solution

The right-hand limit found in part (a) was one, which is positive. This occurred because for x slightly greater than negative one, the function simplified to the constant value one. Since this value stays fixed and never changes sign as x approaches negative one from the right, the answer is positive.

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