The Limit — Question 2

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Question 2

Let the function be defined as: f(x)={x2−4x−2,x<23x−2,x≥2f(x) = \begin{cases} \dfrac{x^2 - 4}{x - 2}, & x < 2 \\ 3x - 2, & x \geq 2 \end{cases}

Determine whether lim⁡x→2f(x)\displaystyle \lim_{x \to 2} f(x) exists. If it does, find its value. Justify your answer.

Original worksheet page 1: question and worked solution for 2-2-002
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Question 2 - Solution

We are asked to evaluate: limx→2f(x)\lim_{x \to 2} f(x) where f(x)={x2−4x−2,x<23x−2,x≥2f(x) = \begin{cases} \dfrac{x^2 - 4}{x - 2}, & x < 2 \\ 3x - 2, & x \geq 2 \end{cases}

Step 1: Evaluate the Left-Hand Limit

For x<2x < 2, f(x)=x2−4x−2=(x−2)(x+2)x−2f(x) = \dfrac{x^2 - 4}{x - 2} = \dfrac{(x - 2)(x + 2)}{x - 2} As long as x≠2x \neq 2, we can cancel x−2x - 2: f(x)=x+2f(x) = x + 2 So: limx→2−f(x)=limx→2−(x+2)=4\lim_{x \to 2^-} f(x) = \lim_{x \to 2^-} (x + 2) = 4

Step 2: Evaluate the Right-Hand Limit

For x≥2x \geq 2, f(x)=3x−2f(x) = 3x - 2, so: limx→2+f(x)=limx→2+(3x−2)=3(2)−2=6−2=4\lim_{x \to 2^+} f(x) = \lim_{x \to 2^+} (3x - 2) = 3(2) - 2 = 6 - 2 = 4

Step 3: Compare One-Sided Limits

limx→2−f(x)=limx→2+f(x)=4⇒limx→2f(x)=4\lim_{x \to 2^-} f(x) = \lim_{x \to 2^+} f(x) = 4 \Rightarrow \lim_{x \to 2} f(x) = \boxed{4}

Conclusion: The limit exists and is equal to 4\boxed{4}.

Original worksheet page 2: question and worked solution for 2-2-002

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