1 Arithmetic Combinations of Functions Do Now: Given f (x) = 2x – 3 and g (x) = x 2 – 1. Find (f + g)(x) and determine the domain.

Copyright © Cengage Learning. All rights reserved. Pre-Calculus Honors 1.5: Combinations of Functions HW: p (8, even, 30, 42, 54, 56, 60)

3 Domain for Combination of Functions Combinations of functions: (f + g)(x), (f – g)(x), (fg)(x), (f/g)(x) Any restrictions on the domain of f and the domain of g must also be considered when forming the sum, difference, product, or quotient of f and g. (As well as the combination.)

4 Compositions of Functions Another way of combining two functions is to form the composition of one with the other. For instance, when f (x) = x 2 and g (x) = x + 1, the composition of f with g is f (g (x)) = f (x + 1) = (x + 1) 2. This composition is denoted as f  g and is read as “f composed with g”.

5 Compositions of Functions Figure 1.50

6 Forming the Composition of f with g Given and g (x) = x – 1, x  1. Evaluate and determine the domain for part c. a.) (f  g)(2) b.) (g  f)(0) c.) (f  g)(x)

7 Forming the Composition of f with g Evaluate (f  g)(x), (g  f)(x), and determine the domain given

8 Do Now: Evaluate the combination of functions. 1.) (f  g)(2)2.) (f + g)(3) x01234 g(x)43210

9 Copyright © Cengage Learning. All rights reserved. Pre-Calculus Honors 1.5: Combinations of Functions HW: p (68, 70, 81, 84, 88)

10 p.55, Example 10 – Bacteria Count The number N of bacteria in a refrigerated petri dish is given by N(T) = 20T 2 – 80T + 500, 2  T  14, where T is the temperature of the petri dish (in degrees Celsius). When the petri dish is removed from refrigeration, the temperature of the petri dish is given by T (t) = 4t + 2, 0  t  3, where t is the time (in hours). a. Find the composition N (T(t)) and interpret its meaning in this context. b. Find the number of bacteria in the petri dish when t = 2 hrs. c. Find the time when the bacteria count reaches 2000.

11 Example 10 – Bacteria Count Solution: a. N (T(t)) = 20(4t + 2) 2 – 80(4t + 2) = 20(16t t + 4) – 320t – = 320t t + 80 – 320t – = 320t The composite function N (T(t)) represents the number of bacteria as a function of the amount of time the petri dish has been out of refrigeration. cont’d

12 Example 10 – Solution b. When t = 2 the number of bacteria is N = 320(2) = = c. The bacteria count will reach N = 2000 when 320t = You can solve this equation for t algebraically as follows. 320t = 2000 cont’d