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Qiuyun TMUA Simulation Test Paper 2 · Q12

Paper 2Logic & proofPowers & logarithms

Now we need to prove:

log⁡ab=ln⁡bln⁡a\log_a b=\frac{\ln b}{\ln a}

How can we choose these steps and prove this statement?

  • (1) Assume ln⁡b=m\ln b=m and ln⁡a=n\ln a=n
  • (2) em=b, en=ae^m=b,\ e^n=a
  • (3) bm=e, an=eb^m=e,\ a^n=e
  • (4) log⁡ab=mn\log_a b=mn
  • (5) log⁡ab=mn\log_a b=\dfrac mn
  • (6) log⁡ab=nm\log_a b=\dfrac nm
  • (7) am/n=ba^{m/n}=b
  • (8) log⁡ab=log⁡enem\log_a b=\log_{e^n}e^m
  • (9) amn=ba^{mn}=b
  • (10) log⁡ab=ln⁡bln⁡a\log_a b=\dfrac{\ln b}{\ln a}
A(1), so (2), so (7), so (5), so (10).
B(1), so (2), so (8), so (4), so (10).
C(1), so (2), so (7), so (4), so (10).
D(1), so (2), so (8), so (5), so (10).
E(1), so (3), so (7), so (4), so (10).
F(1), so (3), so (8), so (5), so (10).

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