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The Function Concept DEFINITION: A function consists of two nonempty sets X and Y and a rule f that associates each element x in X with one and only one.

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Presentation on theme: "The Function Concept DEFINITION: A function consists of two nonempty sets X and Y and a rule f that associates each element x in X with one and only one."— Presentation transcript:

1 The Function Concept DEFINITION: A function consists of two nonempty sets X and Y and a rule f that associates each element x in X with one and only one element y in Y. Read The function f from X into Y and symbolized by f : X Y.

2 X Y f The function f from X into Y F maps X into Y

3 Some examples: Supermarket item price Student chair College student GPA Worker SSN Car license plate number Real number x x 2

4 More examples: Are these functions??? X Y Dormitory roomsStudents Rule: room student(s) assigned Airplane luggage Passengers Rule: piece(s) of luggage passenger Nine digit numbersWorkers Rule: number workers SSN Real numbersReal numbers Rule: x the numbers y such that y 2 = x

5 Another defintion: Let X and Y be sets. A function f from X into Y is a set S of ordered pairs (x,y), x X, y Y, with the property that (x 1, y 1 ) and (x 1, y 2 ) are in S if and only if y 1 = y 2.

6 Examples

7 Some Terminology & Notation Let f : X Y. The set X (the first set) is called the domain of the function. The set of ys in Y which correspond to an element x in X is called the range of the function. The range of f is, in general a subset of Y.

8 Variables: Let f : X Y. The symbols x and y are called variables. In particular, a symbol such as x, representing an arbitrary element in the domain is called an independent variable. A symbol such as y, representing an element in the range corresponding to an element x in the domain is called a dependent variable.

9 Function notation: Let f : X Y. Pick an element x in X and apply the rule f. This produces a unique element in Y. The symbol f(x) is used to denote that element. f(x) is read f of x or the value of f at x or the image of x under f.

10 Another picture XY x f(x)f(x) f

11 More pictures X Y f f(X)f(X) Black box x f(x)f(x) f

12 One-to-one functions: Let f : X Y. f is a one-to-one function if it takes distinct elements in the domain to distinct elements in the range. That is: f is one-to-one if x 1 x 2 implies f(x 1 ) f(x 2 ). Notation: f is 1 – 1.

13 Examples: Which of these function is 1 – 1? Supermarket item price Student GPA Car license plate number f(x) = 2x + 3

14 Inverse functions Suppose f : X Y is 1 – 1. Then there is a function g: f(X) X such that g(f(x)) = x for all x X. g is called the inverse of f and is denoted by f -1 X Y f(X) f g

15 Functions in Mathematics From Geometry and Measurement: 1.Length function: x is a line segment, l(x) = the length of x. 2.Area functions: x is a rectangle, A(x) = the area of x. 3. Volume functions: x is a sphere, V(x) = the volume of x. From Probability & Statistics: E is a subset (event) in a sample space S, P(E) = the probability that E occurs.

16 Functions in Algebra Let f : X Y where X is a given set of real numbers and Y is the set of all real numbers. f is a real-valued function of a real variable Note: The domain X may or may not be the set of all real numbers. Examples:

17 Graph of a function Let f : X Y. The graph of f is the set of points (x, f(x)) plotted in the coordinate plane: Graph of f = {(x, f(x)) | x X }. The graph of f is a geometric object – a picture of the function.

18 Examples:

19 Functions defined on the positive integers: Sequences A function f whose domain is the set of positive integers is called a sequence. The values are called the terms of the sequence; f(1) is the 1 st term, f(2) is the 2 nd term, and so on

20 Subscript notation It is customary to use subscript notation rather than functional notation: and to denote the sequence by a n

21 Examples

22 Recursion formulas A recursion formula or recurrence relation gives a k+1 in terms of one or more of the terms a m that precede a k+1. Examples: Find the first four terms and the nth term for the sequence specified by

23 Solutions

24 More examples (3) List the first six terms of the sequence whose nth term a n is the nth prime number. Give a formula for a n. (4) The first four terms of the sequence a n are: What is the 5 th term?

25 Answers (1) 2, 3, 5, 7, 11, 13; a n = ?????? (2)

26 Limits of sequences Given a sequence a n. What is the behavior of a n for very large n ? That is, as n what can you say about a n ? Examples:

27 Answers (1) 1(2) 0 (3) No limit(4) No limit

28 Two special sequences 1.Arithmetic sequences: A sequence is an arithmetic sequence (arithmetic progression) if successive terms differ by a constant d, called the common difference. That is a n is an arithmetic sequence if

29 Examples Answers: (1) Yes (2) No (3) Yes, assuming the pattern goes on as indicated

30 (4)What is the 12 th term of the arithmetic sequence whose first three terms are: 1, 5, 9?

31 Solving the recursion formula

32 Geometric sequences A geometric sequence is a sequence in which the ratio of successive terms is a nonzero constant r. That is, The number r is called the common ratio.

33 Examples (1)The sequence 8, 4, 2, 1, …. is a geometric sequence. Find the common ratio and give the 5 th term. (2) The sequence is a geometric sequence, find the common ratio and give the 6 th term. (3) a n geometric sequence with common ratio r. Give a formula for a n.

34 Answers:

35 Function defined on intervals Let f : X Y where X is an interval or a union of intervals and Y is the set of real numbers. The graph of f is the set of all points (x,f(x)) in the coordinate plane. The graph of f is the graph of the equation y=f (x).

36 Examples f(x) = 2x + 1 f (x) = x 2 + 1

37 The Elementary Functions 1.The constant functions: The graph of f is a horizontal line c units above or below the x-axis depending on the sign of c. f (x) = 2

38 (2) The identity function and linear functions (a) The function f (x) = x is called the identity function. The graph is

39

40 NONLINEAR FUNCTIONS a > 0a < 0

41 a > 0a < 0

42 (5) Polynomial Functions

43

44 (6) Rational functions

45 Some graphs

46 The Elementary Functions (7) Algebraic functions: sums, differences, products, quotients and roots of rational functions. (8) The trigonometric functions. (9) Exponential functions. (10) Logarithm functions.


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