November 25, 2013 3.1 Exponential and Logistic Functions Exponential Function: f(x) = a b where: x a (initial value) is a nonzero real number *occurs when x = 0 b (base) is positive, and b ≠1 Which are exponential functions? a. f(x)=5x b. f(x)=3x2 c. f(x)=4x-3 d. f(x)=7 2-x November 25, 2013 Determine the formulas for g(x) and h(x). Values for Two Exponential Functions x g(x) h(x) -2 4/9 128 -1 4/3 32 0 4 8 1 12 2 2 36 1/2 November 25, 2013 Exponential Growth and Decay x For any exponential function f(x) = a b and any real number x, If a > 0 and b > 1, the function is increasing (exponential growth) and b is the growth factor. If a > 0 and b < 1, the function is decreasing (exponential decay) and b is the decay factor. November 25, 2013 Exploration #1 (pg. 279) domain: ________________ range: _________________ continuity: _______________ incr/decr: ________________ symmetry: ________________ boundedness: ______________ extrema: _________________ asymptotes: _______________ end behavior: ______________ November 25, 2013 Describe how each graph is transformed from f(x) = 5x. a. g(x) = 5x+1 b. h(x) = 5-x c. k(x) = 3 5x November 25, 2013 f(x) = 1+ 1 x x x 10 1 x (1+ x ) 100 1000 10,000 100,000 November 25, 2013 The Natural Base e. e = lim x ∞ 1 + 1 x x November 25, 2013 Exponential Functions and the Base e. Any exponential function f(x) = a b f(x) = a ekx x can be rewritten as for an appropriately chosen real number k. If a > 0 and k > 0, f(x) is an exp. growth fn. If a > 0 and k < 0, f(x) is an exp. decay fn. Ex. 1. Graph f(x) = 2x. 2. Overlay the graphs for 0.7, and 0.8. g(x) = ekx for k=0.4, 0.5, 0.6, 3. For which value of k does the graph of g most closely match the graph of f? 4. Using tables, find the 3-decimal-place value of k for which the values of g most closely approximate the values of f. November 25, 2013 The number B of bacteria in a petri dish culture after t hours is given by 0.693t B = 100e a. What was the initial number of bacteria present? b. How many bacteria are present after 6 hours? November 25, 2013 Logistic Growth Functions: f(x) = where c 1 + a bx or f(x) = c 1 + a e-kx a,b,c, and k are postive, with b < 1 c is the limit to growth If a = c = k = 1, then we get the logistic growth function f(x) = 1 1 + e-x November 25, 2013 Graph the function. Find the y-intercept and horizontal asymptotes. 18 f(x) = 1 + 5(0.2)x November 25, 2013 Write the logistic function that satisfies the given information. initial value = 12, limit to growth = 60, passing through (1,24) November 25, 2013 Graph and find the y-int. and horizontal asymptotes. 1. f(x) = 20 1 + 2e-3x
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