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Right-hand limit at x = 3

Consider the function f(x)=x2−5x+6∣x−3∣f(x) = \dfrac{x^2 - 5x + 6}{|x-3|} defined for all x≠3x \neq 3. We want to investigate the behavior of f(x)f(x) as xx approaches 33.

Simplify f(x)f(x) for x>3x > 3 (where ∣x−3∣=x−3|x-3| = x-3), and use this to find lim⁡x→3+f(x).\lim_{x \to 3^+} f(x).

Hint

Factor the numerator as x2−5x+6=(x−2)(x−3)x^2 - 5x + 6 = (x-2)(x-3), then replace ∣x−3∣|x-3| with x−3x-3 since x>3x > 3. Cancel the common factor before taking the limit.

Step-by-step solution

Factor the numerator: x2−5x+6=(x−2)(x−3)x^2 - 5x + 6 = (x-2)(x-3). For x>3x > 3, we have x−3>0x - 3 > 0, so ∣x−3∣=x−3|x-3| = x-3. Thus for x>3x > 3, f(x)=(x−2)(x−3)x−3=x−2.f(x) = \frac{(x-2)(x-3)}{x-3} = x-2.

Since f(x)=x−2f(x) = x - 2 for all xx near 33 from the right, the right-hand limit is found by direct substitution into this simplified expression: lim⁡x→3+f(x)=3−2=1.\lim_{x\to 3^+} f(x) = 3 - 2 = 1.

Left-hand limit at x = 3

Simplify f(x)f(x) for x<3x < 3 (where ∣x−3∣=3−x|x-3| = 3-x), and use this to find lim⁡x→3−f(x).\lim_{x \to 3^-} f(x).

Hint

For x<3x < 3, x−3x - 3 is negative, so ∣x−3∣=−(x−3)=3−x|x - 3| = -(x-3) = 3 - x. Substitute this into the simplified factored form of ff.

Step-by-step solution

As before, x2−5x+6=(x−2)(x−3)x^2 - 5x + 6 = (x-2)(x-3). For x<3x < 3, we have x−3<0x - 3 < 0, so ∣x−3∣=−(x−3)=3−x|x - 3| = -(x-3) = 3-x. Thus for x<3x < 3, f(x)=(x−2)(x−3)−(x−3)=−(x−2)=2−x.f(x) = \frac{(x-2)(x-3)}{-(x-3)} = -(x-2) = 2-x.

Since f(x)=2−xf(x) = 2 - x for all xx near 33 from the left, direct substitution gives lim⁡x→3−f(x)=2−3=−1.\lim_{x\to 3^-} f(x) = 2 - 3 = -1.

Existence of the two-sided limit

Based on your results from the previous two parts, does lim⁡x→3f(x)\displaystyle\lim_{x \to 3} f(x) exist? If it exists, state its value; if not, explain why not.

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→3+f(x)=1\lim_{x\to 3^+} f(x) = 1, and from part (b), lim⁡x→3−f(x)=−1\lim_{x\to 3^-} f(x) = -1. These two one-sided limits are not equal to each other.

Since the left-hand and right-hand limits disagree, the two-sided limit lim⁡x→3f(x)\lim_{x\to 3} f(x) does not exist.

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