Chabot Mathematics §2.3 Algebra of Functions Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu Chabot College Mathematics 1 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Review § 2.2 MTH 55 Any QUESTIONS About • §2.2 → Function Graphs Any QUESTIONS About HomeWork • §2.2 → HW-04 Chabot College Mathematics 2 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Function ReVisited A FUNCTION is a special kind of Correspondence between two sets. The first set is called the Domain. The second set is called the Range. For any member of the domain, there is EXACTLY ONE member of the range to which it corresponds. This kind of correspondence is called a function Domain Chabot College Mathematics 3 Correspondence Range Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Function Analogy → Machinery The function pictured has been named f. Here x represents an arbitrary input, and f(x) (read “f of x,” “f at x,” or “the value of “f at x”) represents the corresponding output. Chabot College Mathematics 4 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Implicit Domain If the domain of a function that is defined by an equation is not explicitly specified, then we take the domain of the function to be the LARGEST SET OF REAL NUMBERS that result in REAL NUMBERS AS OUTPUTS. • i.e., DEFAULT Domain is all x’s that produce VALID Functional RESULTS Chabot College Mathematics 5 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Example Find Function Domain Find the domain of the Function 2 f ( x) . x 8 First determine if there is/are any number(s) x for which the function cannot be computed?” Chabot College Mathematics 6 Recall that an expression is meaningless for Division by Zero So In this case the Fcn CanNot be computed when x−8=0 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Example Find Function Domain This Fcn Undefined for x − 8 = 0 2 f ( x) . x 8 To determine what x-value would cause x − 8 to be 0, we solve the equation: Thus 8 is not in the domain of f, whereas all other real numbers are. Then the domain of f is x | x is a Real No. and x 8 x 8 0 x 8 Chabot College Mathematics 7 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Algebra of Functions The Sum, Difference, Product, or Quotient of Two Functions Suppose that a is in the domain of two functions, f and g. The input a is paired with f(a) by f and with g(a) by g. The outputs can then be added to obtain: f(a) + g(a). Chabot College Mathematics 8 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Algebra of Functions If f and g are functions and x is in the domain of both functions, then the “Algebra” for the two functions: 1. ( f 2. ( f 3. ( f 4. ( f g )( x) f ( x) g ( x); g )( x) f ( x) g ( x); g )( x) f ( x) g ( x); g )( x) f ( x) g ( x), provided g ( x) 0. Chabot College Mathematics 9 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Example Function Algebra Find the Following for these Functions f ( x) 2 x x and g ( x) 3x 1, 2 • a) (f + g)(4) b) (f − g)(x) • c) (f/g)(x) d) (f•g)(−1) SOLUTION a) Since f(4) = −8 and g(4) = 13, we have (f + g)(4) = f(4) + g(4) = −8 + 13 = 5. Chabot College Mathematics 10 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Example Function Algebra 2 f ( x ) 2 x x and g ( x) 3x 1, SOLUTION for b) (f − g)(x) → ( f g )( x) f ( x) g ( x) 2 x x (3x 1) 2 x x 1. c) (f/g)(x) → ( f / g )( x) f ( x) / g ( x) 2 2x x . 3x 1 2 Assumes 1 x 3 Chabot College Mathematics 11 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Example Function Algebra 2 f ( x ) 2 x x and g ( x) 3x 1, SOLUTION for d) (f•g)(−1) → f(−1) = −3 and g(−1) = −2, so ( f g )(1) f (1) g (1) (3)(2) 6. Chabot College Mathematics 12 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Example Function Algebra Given f(x) = x2 + 2 and g(x) = x − 3, find each of the following. • a) The domain of f + g, f − g, f•g, and f/g • b) (f − g)(x) c) (f/g)(x) SOLUTION a) • The domain of f is the set of all real numbers. The domain of g is also the set of all real numbers. The domains of f +g, f − g, and f•g are the set of numbers in the intersection of the domains; i.e., the set of numbers in both domains, or all real No.s • For f/g, we must exclude 3, since g(3) = 0 Chabot College Mathematics 13 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Example Function Algebra SOLUTION b) → (f − g)(x) • (f − g)(x) = f(x) − g(x) = (x2 + 2) − (x − 3) = x2 − x + 5 SOLUTION c) → (f/g)(x) f ( x) ( f / g )( x) g ( x) • Remember to add the restriction that x ≠ 3, since 3 is not in the domain of (f/g)(x) Chabot College Mathematics 14 x 2 x3 2 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp WhiteBoard Work Problems From §2.3 Exercise Set • 56 by PPT, 10, 30, 36, 42, 64 Demographers use birth and death rates to determine population growth and evaluate the general health of the populations they study. These rates usually denote the number of births and deaths per 1,000 people in a given year. Chabot College Mathematics 15 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp P2.3-56 Functions by Graphs 6 5 y f x From the Graph the fcn T-table y 4 3 2 x 1 0 -6 -5 -4 -3 -2 y g x -1 0 -1 -2 -3 -4 -5 M55_§2.2_Graphs_0806.xls Chabot College Mathematics 16 1 2 3 4 5 6 x -5 -4 -3 -2 -1 0 1 2 3 4 5 f(x) g(x) -1 5 0 4 1 3 2 3 2 2 0 1 1 -1 1 -3 -1 -2 -6 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp P2.3-56 Graph (f − g)(x) Recall from Lecture 6 y y1 f x 5 • (f − g)(x) = f(x) − g(x) 4 3 Next Use for Plotting • y1 = f(x) • y2 = g(x) 2 -6 -5 -4 -3 -2 0 -1 1 2 3 4 5 -1 -2 -3 -4 • f(x) − g(x) = y1 − y2 -5 M55_§2.2_Graphs_0806.xls 17 x 0 Thus for Plot Chabot College Mathematics y2 g x 1 -6 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp 6 P2.3-56 Graph (f − g)(x) Recall from Lecture • (f − g)(x) = f(x) − g(x) Use the above relation to construct (f − g)(x) T-Table • Can only Calc f(x) – g(x) where Domains OverLap Chabot College Mathematics 18 x -5 -4 -3 -2 -1 0 1 2 3 4 5 f(x) g(x) -1 5 0 4 1 3 2 3 2 2 0 1 1 -1 1 -3 -1 -2 f(x) - g(x) No Domain 5 3 1 1 2 0 -2 No Domain No Domain No Domain Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp y 5 4 y f g x 3 y g x 2 1 x 0 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 -1 -2 -3 -4 y f x -5 M55_§2.2_Graphs_0806.xls Chabot College Mathematics 19 -6 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp P2.3-56 (f – g)(x) Graph 6 All Done for Today Fcn Algebra By MicroProcessor Chabot College Mathematics 20 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp Chabot Mathematics Appendix r s r s r s 2 2 Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu – Chabot College Mathematics 21 Bruce Mayer, PE File = MTH55_Lec-04_ec_2-2_Fcn_Algebra.pp