Continuity — Question 3

PDF ↗

Question 3

Let the function f(x)f(x) be defined by: f(x)={x2−4x−2,x≠2k,x=2f(x) = \begin{cases} \dfrac{x^2 - 4}{x - 2}, & x \neq 2 \\ k, & x = 2 \end{cases}

Determine the value of kk such that f(x)f(x) is continuous at x=2x = 2.

Original worksheet page 1: question and worked solution for 2-9-003
Show solutionHide solution

Question 3 - Solution

We are given: f(x)={x2−4x−2,x≠2k,x=2f(x) = \begin{cases} \dfrac{x^2 - 4}{x - 2}, & x \neq 2 \\ k, & x = 2 \end{cases}

To make f(x)f(x) continuous at x=2x = 2, the following condition must hold: limx→2f(x)=f(2)\lim_{x \to 2} f(x) = f(2)

Step 1: Compute the limit as x→2x \to 2

Factor the numerator: x2−4=(x−2)(x+2)x^2 - 4 = (x - 2)(x + 2)

For x≠2x \neq 2, the function simplifies to: f(x)=x+2f(x) = x + 2

So, limx→2f(x)=limx→2(x+2)=4\lim_{x \to 2} f(x) = \lim_{x \to 2} (x + 2) = 4

Step 2: Match the function value

Continuity requires: f(2)=k=4f(2) = k = 4

Final Answer: k=4\boxed{k = 4}

Original worksheet page 2: question and worked solution for 2-9-003

Original worksheet layout. Use Enlarge or open the PDF for a closer view.