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1.7 Rational exponents, laws of logarithms and exponential equationsIB Maths: Analysis and Approaches SL: Subtopic test

10 questions, 27 marks

IB Maths: Analysis and Approaches SL

1.7 Rational exponents, laws of logarithms and exponential equations

Total 27 marks

Name

Class

Date

  1. 1
    Let a=2723a = 27^{\frac{2}{3}} and b=16−34b = 16^{-\frac{3}{4}}.
    (a)
    Find the value of aa.
    [1 mark]
    • A1818
    • B8181
    • C99
    • D19\frac{1}{9}
    (b)
    Find the value of bb.
    [1 mark]
    • A18\frac{1}{8}
    • B88
    • C−8-8
    • D−12-12
    (c)
    Find the exact value of ab\dfrac{\sqrt{a}}{b}.
    [2 marks]

    Total for question 1: 4 marks

  2. 2
    It is given that log⁡2x=p\log_2 x = p and log⁡2y=q\log_2 y = q, where x>0x > 0 and y>0y > 0.
    (a)
    Find an expression for log⁡2(8x3)\log_2\left(8x^3\right) in terms of pp.
    [1 mark]
    • A8+3p8+3p
    • B3+3p3+3p
    • C24p24p
    • D3+p33+p^3
    (b)
    Find an expression for log⁡2(xy)\log_2\left(\dfrac{\sqrt{x}}{y}\right) in terms of pp and qq.
    [1 mark]
    • Ap−q\sqrt{p}-q
    • Bp2q\frac{p}{2q}
    • Cp−q2\frac{p-q}{2}
    • Dp2−q\frac{p}{2}-q
    (c)
    Use the change of base formula to express log⁡8y\log_8 y in terms of qq.
    [2 marks]

    Total for question 2: 4 marks

  3. 3
    The number of bacteria, NN, in a laboratory culture tt hours after the start of an experiment is modelled by N=500×2t3N = 500\times2^{\frac{t}{3}}, for t≥0t\ge0.
    (a)
    Find the time taken for the number of bacteria to reach 4000.
    [3 marks]
    (b)
    Show that the exact time taken for the number of bacteria to reach 3000 is 3+3log⁡233 + 3\log_2 3 hours.
    [4 marks]

    Total for question 3: 7 marks

  4. 4
    The functions ff and gg are defined for x∈Rx\in\mathbb{R} by f(x)=2x+1f(x) = 2^{x+1} and g(x)=3x−1g(x) = 3^{x-1}.
    (a)
    Solve the equation f(x)=g(x)f(x) = g(x), giving your answer in the form x=ln⁡pln⁡qx = \dfrac{\ln p}{\ln q}, where p,q∈Qp, q\in\mathbb{Q}.
    [6 marks]
    (b)
    (i) Show that f(x) g(x)=23×6xf(x)\,g(x) = \frac{2}{3}\times6^{x}.
    (ii) Hence solve
    f(x) g(x)=12f(x)\,g(x) = 12, giving your answer in the form x=1+log⁡6kx = 1+\log_6 k, where k∈Zk\in\mathbb{Z}.
    [6 marks]

    Total for question 4: 12 marks

End of questions