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Determine the continuity of the function f(x) at x=3, where f(x) = (x3 − 27)/(x2 - 9) for x != 3 and f(x) = 5 for x = 3.

Mathematics

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Graph of f(x) = (x³ − 27)/(x² − 9)

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Key points of f(x) = (x³ − 27)/(x² − 9)
Pointxy
Maximum−6−9
Minimum03

Step-by-step solution

3 steps

The image contains multiple questions. I will solve question 4.a.

a asks to determine the continuity of the given function f(x)f(x) at x=3x=3.
The function is defined as:

f(x)={x3−27x2−9for x≠35for x=3f(x) = \begin{cases} \frac{x^3 - 27}{x^2 - 9} & \text{for } x \neq 3 \\ 5 & \text{for } x = 3 \end{cases}

For a function to be continuous at a point 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).
  1. Check if f(3)f(3) is defined.

    From the definition of f(x)f(x), when x=3x=3, f(x)=5f(x)=5.
    So, f(3)=5f(3) = 5. The function is defined at x=3x=3.

  2. Evaluate the limit lim⁡x→3f(x)\lim_{x \to 3} f(x).

    For x≠3x \neq 3, f(x)=x3−27x2−9f(x) = \frac{x^3 - 27}{x^2 - 9}.
    We can factor the numerator and denominator.
    The numerator is a difference of cubes: a3−b3=(a−b)(a2+ab+b2)a^3 - b^3 = (a-b)(a^2 + ab + b^2).
    So, x3−27=x3−33=(x−3)(x2+3x+9)x^3 - 27 = x^3 - 3^3 = (x-3)(x^2 + 3x + 9).
    The denominator is a difference of squares: a2−b2=(a−b)(a+b)a^2 - b^2 = (a-b)(a+b).
    So, x2−9=x2−32=(x−3)(x+3)x^2 - 9 = x^2 - 3^2 = (x-3)(x+3).

    Now, substitute these factored forms into the limit expression:

    lim⁡x→3x3−27x2−9=lim⁡x→3(x−3)(x2+3x+9)(x−3)(x+3)\lim_{x \to 3} \frac{x^3 - 27}{x^2 - 9} = \lim_{x \to 3} \frac{(x-3)(x^2 + 3x + 9)}{(x-3)(x+3)}

    Since x→3x \to 3, x≠3x \neq 3, so x−3≠0x-3 \neq 0. We can cancel the (x−3)(x-3) terms.

    lim⁡x→3x2+3x+9x+3\lim_{x \to 3} \frac{x^2 + 3x + 9}{x+3}

    Now, substitute x=3x=3 into the simplified expression:

    32+3(3)+93+3=9+9+96=276\frac{3^2 + 3(3) + 9}{3+3} = \frac{9 + 9 + 9}{6} = \frac{27}{6}

    Simplify the fraction:

    276=92\frac{27}{6} = \frac{9}{2}

    So, lim⁡x→3f(x)=92\lim_{x \to 3} f(x) = \frac{9}{2}.

  3. Compare lim⁡x→3f(x)\lim_{x \to 3} f(x) with f(3)f(3).

    We found f(3)=5f(3) = 5 and lim⁡x→3f(x)=92\lim_{x \to 3} f(x) = \frac{9}{2}.
    Since 5≠925 \neq \frac{9}{2}, the third condition for continuity is not met.

    Therefore, the function f(x)f(x) is not continuous at x=3x=3.

    The function f(x)f(x) is not continuous at x=3x=3 because lim⁡x→3f(x)≠f(3)\lim_{x \to 3} f(x) \neq f(3).

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