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Base e and Natural Logarithms
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History The number e is a famous irrational number, and is one of the most important numbers in mathematics. The first few digits are 2.7182818284590452353602874713527... It is often called Euler's number after Leonhard Euler. e is the base of the natural logarithms (invented by John Napier).
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Calculating The value of (1 + 1/n) n approaches e as n gets bigger and bigger: n (1 + 1/n) n 12.00000 22.25000 52.48832 102.59374 1002.70481 1,0002.71692 10,0002.71815 100,0002.71827
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Vocabulary natural base: the number e, which is found using the base rate of growth shared by all continually growing processes Used heavily in science to model quantities that grow & decay continuously natural base exponential function: an exponential function with base e
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Vocabulary natural logarithm: a logarithm with base e The natural log gives you the time needed to reach a certain level of growth. natural logarithmic function: the inverse of the natural base exponential function
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Ex 1 Use a calculator to estimate to four decimal places. Ex 2 Ex 3 Ex 4
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Ex 5 Exponential logarithmic Write an equivalent equation in the other form. Ex 6 Writing Equivalent Expressions Ex 8 Ex 7
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Inverse Properties
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Ex 9 Evaluate Ex 11 Writing Equivalent Expressions Evaluate Ex 10 Evaluate Ex 12
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Solving Equations Ex 13 Solve the following equations. Ex 14
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Solving Equations Ex 15 Solve the following equations. Ex 16
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Graphing properties ( and lnx are inverse functions reflected in y=x) These can be transformed (stretched, translated and reflected) in the same way as other functions. But, be careful of the hidden asymptotes!
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Examination-style question The function f is defined by a)Describe the sequence of geometrical transformations by which the graph of y = 3 e x + 1 – 4 can be obtained from that of y = e x. b)The graph of y = f ( x ) crosses the y -axis at point A and the x -axis at point B. Write down the coordinates of A and B, working to 2 decimal places. c)Write an expression for f –1 ( x ) and state its domain and range. d)Sketch the graphs of y = f ( x ) and y = f –1 ( x ) on the same set of axes and state their geometrical relationship.
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Examination-style question d) y = f –1 ( x ) is a reflection of y = f ( x ) in the line y = x. y = x x y y = –4 y = f ( x ) y = f –1 ( x ) x = –4 (–0.71, 0) (0, –0.71) (0, 4.15) (4.15, 0)
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