15.1 Natural log: ln
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Natural log: ln


• Definition of `` natural logarithm"" and mathematical constant ``e":":

Recall: common logarithms = log with base 10"``10"
example:log3=log103 \log3 = \log_{10}3
natural logarithms = log with base ``e""
example:ln5=loge5 \ln5 = \log_e5

Like π"``\pi" , a mathematical constant equal to 3.14….., `` e"" is just another mathematical constant equal to 2.71…. .

Significance of π"``\pi" : we use it in circle calculations:
example: areacircle=πr2 area_{circle} = \pi r^2
circumferencecircle=2πr circumference_{circle} = 2 \pi r
Significance of ``e"" : we use it mostly in calculus. `` e"" is a unique number such that the slope of tangent line at every point on the graph of f(x)=ex f(x) = e^x is equal to the y-value of the point.

    • a)
      by using the LOG key on a calculator.
    • b)
      by using the LN key on a calculator.
  • 2.
    Without using a calculator, evaluate:
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Natural log: ln

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