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Evaluate the limit _x 3 (x2 - 9)/(x2 - 2x - 3) and determine if the function f(x) is continuous at x=2. If not, identify the type of discontinuity.

Mathematics

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Here are the solutions to the questions on limits and continuity:

  1. Evaluate the limit

    lim⁡x→3x2−9x2−2x−3\lim_{x \to 3} \frac{x^2 - 9}{x^2 - 2x - 3}
  2. Substitute x=3x=3 into the expression to check for an indeterminate form.

    32−932−2(3)−3=9−99−6−3=00\frac{3^2 - 9}{3^2 - 2(3) - 3} = \frac{9 - 9}{9 - 6 - 3} = \frac{0}{0}

    Since we have an indeterminate form, we need to simplify the expression.

  3. Factor the numerator and the denominator.

    The numerator is a difference of squares: x2−9=(x−3)(x+3)x^2 - 9 = (x-3)(x+3).
    The denominator is a quadratic: x2−2x−3=(x−3)(x+1)x^2 - 2x - 3 = (x-3)(x+1).

  4. Substitute the factored forms into the limit expression and cancel common factors.

    lim⁡x→3(x−3)(x+3)(x−3)(x+1)\lim_{x \to 3} \frac{(x-3)(x+3)}{(x-3)(x+1)}

    Since x→3x \to 3, x≠3x \neq 3, so we can cancel the (x−3)(x-3) terms.

    lim⁡x→3x+3x+1\lim_{x \to 3} \frac{x+3}{x+1}
  5. Substitute x=3x=3 into the simplified expression.

    3+33+1=64=32\frac{3+3}{3+1} = \frac{6}{4} = \frac{3}{2}

    The limit is ∗32∗\boxed*{\frac{3}{2}}*.

  6. Determine if the following function is continuous at x=2x=2.

    If not, identify the type of discontinuity.

    f(x)={x2−4x−2if x≠23if x=2f(x) = \begin{cases} \frac{x^2 - 4}{x-2} & \text{if } x \neq 2 \\ 3 & \text{if } x = 2 \end{cases}

    For a function to be continuous at x=cx=c, three conditions must be met:

    1. f(c)f(c) must be defined.
    2. lim⁡x→cf(x)\lim_{x \to c} f(x) must exist.
    3. lim⁡x→cf(x)=f(c)\lim_{x \to c} f(x) = f(c).
  7. Check if f(2)f(2) is defined.

    From the definition of the function, f(2)=3f(2) = 3. So, f(2)f(2) is defined.

  8. Evaluate the limit lim⁡x→2f(x)\lim_{x \to 2} f(x).

    For x≠2x \neq 2, f(x)=x2−4x−2f(x) = \frac{x^2 - 4}{x-2}.

    lim⁡x→2x2−4x−2\lim_{x \to 2} \frac{x^2 - 4}{x-2}

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

    lim⁡x→2(x−2)(x+2)x−2\lim_{x \to 2} \frac{(x-2)(x+2)}{x-2}

    Cancel the (x−2)(x-2) terms since x≠2x \neq 2.

    lim⁡x→2(x+2)\lim_{x \to 2} (x+2)

    Substitute x=2x=2:

    2+2=42+2 = 4

    So, lim⁡x→2f(x)=4\lim_{x \to 2} f(x) = 4. The limit exists.

  9. Compare f(2)f(2) and lim⁡x→2f(x)\lim_{x \to 2} f(x).

    We have f(2)=3f(2) = 3 and lim⁡x→2f(x)=4\lim_{x \to 2} f(x) = 4.
    Since f(2)≠lim⁡x→2f(x)f(2) \neq \lim_{x \to 2} f(x), the function is not continuous at x=2x=2.

  10. Identify the type of discontinuity.

    Since the limit lim⁡x→2f(x)\lim_{x \to 2} f(x) exists but is not equal to f(2)f(2), this is a removable discontinuity. If we redefined f(2)f(2) to be 4 instead of 3, the discontinuity would be removed.

    The function is not continuous at x=2x=2. It has a removable discontinuity\boxed{\text{removable discontinuity}}.

  11. Find the value of kk that makes the function continuous at x=1x=1.

    g(x)={2x+kif x≤15−xif x>1g(x) = \begin{cases} 2x + k & \text{if } x \le 1 \\ 5 - x & \text{if } x > 1 \end{cases}

    For g(x)g(x) to be continuous at x=1x=1, the left-hand limit, the right-hand limit, and the function value at x=1x=1 must all be equal.

    lim⁡x→1−g(x)=lim⁡x→1+g(x)=g(1)\lim_{x \to 1^-} g(x) = \lim_{x \to 1^+} g(x) = g(1)
  12. Find g(1)g(1).

    Using the first part of the piecewise function for x≤1x \le 1:

    g(1)=2(1)+k=2+kg(1) = 2(1) + k = 2 + k
  13. Find the left-hand limit, lim⁡x→1−g(x)\lim_{x \to 1^-} g(x).

    For x<1x < 1, g(x)=2x+kg(x) = 2x + k.

    lim⁡x→1−(2x+k)=2(1)+k=2+k\lim_{x \to 1^-} (2x + k) = 2(1) + k = 2 + k
  14. Find the right-hand limit, lim⁡x→1+g(x)\lim_{x \to 1^+} g(x).

    For x>1x > 1, g(x)=5−xg(x) = 5 - x.

    lim⁡x→1+(5−x)=5−1=4\lim_{x \to 1^+} (5 - x) = 5 - 1 = 4
  15. Set the limits and function value equal to solve for kk.

    For continuity, we must have:

    2+k=42 + k = 4

    Subtract 2 from both sides:

    k=4−2k = 4 - 2 k=2k = 2

    The value of kk that makes the function continuous at x=1x=1 is 2\boxed{2}.

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