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5.13 Limits and l'Hôpital's ruleIB Maths: Analysis and Approaches HL: Subtopic test

10 questions, 27 marks

IB Maths: Analysis and Approaches HL

5.13 Limits and l'Hôpital's rule

Total 27 marks

Name

Class

Date

  1. 1
    Let f(x)=e3x−1f(x) = e^{3x} - 1 and g(x)=sin⁡2xg(x) = \sin 2x, for x∈Rx \in \mathbb{R}.
    (a)
    Find lim⁡x→0f(x)g(x)\lim_{x \to 0}\dfrac{f(x)}{g(x)}.
    [1 mark]
    • A32\dfrac{3}{2}
    • B23\dfrac{2}{3}
    • C33
    • D00
    (b)
    Find lim⁡x→0f(x)−3xx2\lim_{x \to 0}\dfrac{f(x) - 3x}{x^{2}}.
    [1 mark]
    • A99
    • B32\dfrac{3}{2}
    • C92\dfrac{9}{2}
    • DThe limit does not exist.
    (c)
    Find lim⁡x→0g(x)f(2x)\lim_{x \to 0}\dfrac{g(x)}{f(2x)}.
    [2 marks]

    Total for question 1: 4 marks

  2. 2
    Consider the functions defined for x>0x > 0 by u(x)=x2e−xu(x) = x^{2}e^{-x}, v(x)=5x2−3x2x2+ln⁡xv(x) = \dfrac{5x^{2} - 3x}{2x^{2} + \ln x} and w(x)=xln⁡xw(x) = x\ln x.
    (a)
    Find lim⁡x→∞u(x)\lim_{x \to \infty} u(x).
    [1 mark]
    • A22
    • B11
    • C∞\infty
    • D00
    (b)
    Find lim⁡x→∞v(x)\lim_{x \to \infty} v(x).
    [1 mark]
    • A00
    • B52\dfrac{5}{2}
    • C∞\infty
    • D55
    (c)
    By writing w(x)w(x) as a quotient, find lim⁡x→0+w(x)\lim_{x \to 0^{+}} w(x).
    [2 marks]

    Total for question 2: 4 marks

  3. 3
    A bank pays a nominal annual interest rate of 6%, compounded nn times per year. An investment of £1000 grows to £AnA_{n} after one year, where An=1000(1+0.06n)nA_{n} = 1000\left(1 + \dfrac{0.06}{n}\right)^{n}. In this question nn may be treated as a continuous variable.
    (a)
    Show that lim⁡n→∞nln⁡(1+0.06n)=0.06\lim_{n \to \infty} n\ln\left(1 + \dfrac{0.06}{n}\right) = 0.06.
    [3 marks]
    (b)
    Hence find, in exact form, the limiting value of AnA_{n} as n→∞n \to \infty, and interpret this value in context. Use your calculator to find by how much this limiting value exceeds the amount after one year when interest is compounded once a year.
    [4 marks]

    Total for question 3: 7 marks

  4. 4
    This question is about limits as x→0x \to 0 in which the numerator and the denominator both tend to 00. The Maclaurin series for exe^{x} is 1+x+x22!+x33!+⋯1 + x + \dfrac{x^{2}}{2!} + \dfrac{x^{3}}{3!} + \cdots.
    (a)
    Use l'Hôpital's rule to find lim⁡x→0x−sin⁡xx3\lim_{x \to 0}\dfrac{x - \sin x}{x^{3}}, showing clearly that the rule may be applied at each stage.
    [6 marks]
    (b)
    It is given that lim⁡x→0eax−1−2xx2\lim_{x \to 0}\dfrac{e^{ax} - 1 - 2x}{x^{2}} exists and is finite, where aa is a constant. Use the Maclaurin series for exe^{x} to find the value of aa and the value of the limit.
    [6 marks]

    Total for question 4: 12 marks

End of questions