Definition-of-a-Relation一个的关系的定义-课件.ppt--（课件中不含音视频）

1、Definition of a RelationA relation is any set of ordered pairs.The set of all first components of the ordered pairs is called the domain of the relation,and the set of all second components is called the range of the relation.Example:Analyzing U.S.Mobile-Phone Bills as a RelationSolutionThe domain i

2、s the set of all first components.Thus,the domain is 1994,2019,2019,2019,2019.The range is the set of all second components.Thus,the range is56.21,51.00,47.70,42.78,39.43.Find the domain and range of the relation(1994,56.21),(2019,51.00),(2019,47.70),(2019,42.78),(2019,39.43)Definition of a Function

3、A function is a correspondence between two sets X and Y that assigns to each element x of set X exactly one element y of set Y.For each element x in X,the corresponding element y in Y is called the value of the function at x.The set X is called the domain of the function,and the set of all function

4、values,Y,is called the range of the function.Example:Determining Whether a Relation is a FunctionSolutionWe begin by making a figure for each relation that shows set X,the domain,and set Y,the range,shown below.Determine whether each relation is a function.a.(1,6),(2,6),(3,8),(4,9)b.(6,1),(6,2),(8,3

5、),(9,4)1234689DomainRange(a)Figure(a)shows that every element in the domain corresponds to exactly one element in the range.No two ordered pairs in the given relation have the same first component and different second components.Thus,the relation is a function.6891234DomainRange(b)Figure(b)shows tha

6、t 6 corresponds to both 1 and 2.This relation is not a function;two ordered pairs have the same first component and different second components.When is a relation a function?T=(1,2),(3,4),(6,5),(1,5)Note that the first component in the first pair is the same as the first component in the second pair

7、,therefore T is not a function.Determine whether each relation is a function.S=(1,2),(3,4),(5,6),(7,8)Each first component is unique,therefore S is a functionFunction NotationWhen an equation represents a function,the function is often named by a letter such as f,g,h,F,G,or H.Any letter can be used

8、to name a function.Suppose that f names a function.Think of the domain as the set of the functions inputs and the range as the set of the functions outputs.The input is represented by x and the output by f(x).The special notation f(x),read f of x or f at x,represents the value of the function at the

9、 number x.If a function is named f and x represents the independent variable,the notation f(x)corresponds to the y-value for a given x.Thus,f(x)=4-x2 and y=4-x2 define the same function.This function may be written asy=f(x)=4-x2.Example:Evaluating a FunctionSolutionWe substitute 2,x+3,and-x for x in

10、 the definition of f.When replacing x with a variable or an algebraic expression,you might find it helpful to think of the functions equation asf(x)=x2+3x+5.If f(x)=x2+3x+5,evaluate:a.f(2)b.f(x+3)c.f(-x)a.We find f(2)by substituting 2 for x in the equation.f(2)=22+3 2+5=4+6+5=15Thus,f(2)=15.moremore

11、Example:Evaluating a FunctionSolutionb.We find f(x+3)by substituting x+3 for x in the equation.f(x+3)=(x+3)2+3(x+3)+5If f(x)=x2+3x+5,evaluate:a.f(2)b.f(x+3)c.f(-x)Equivalently,f(x+3)=(x+3)2+3(x+3)+5=x2+6x+9+3x+9+5=x2+9x+23.Square x+3 and distribute 3 throughout the parentheses.moremoreExample:Evalua

12、ting a FunctionSolutionc.We find f(-x)by substituting-x for x in the equation.f(-x)=(-x)2+3(-x)+5If f(x)=x2+3x+5,evaluate:a.f(2)b.f(x+3)c.f(-x)Equivalently,f(-x)=(-x)2+3(-x)+5 =x2 3x+5.Finding a Functions DomainIf a function f does not model data or verbal conditions,its domain is the largest set of

13、 real numbers for which the value of f(x)is a real number.Exclude from a functions domain real numbers that causedivision by zero and real numbers that result in an even root of a negative number.Example:Finding the Domain of a FunctionSolutionNormally it is safe to say the domain of a function is a

14、ll real numbers.However,there are 2 conditions which must be considered:1)division by zero and 2)even roots of negative numbers.Consider the following functions and find the domain of each function:a.The function f(x)=x2 7x contains neither division nor an even root.The domain of f is the set of all

15、 real numbers.moremore2.()7af xxx26.()9xbg xx.()312c h xxb.The function contains division.Because division by 0 is undefined,we must exclude from the domain values of x that cause x2 9 to be 0.Thus,x cannot equal 3 or 3.The domain of function g is x|x=-3,x=3./96)(2xxxgExample:Finding the Domain of a

16、 FunctionSolutionContinuing c.The function contains an even root.Because only nonnegative numbers have real square roots,the quantity under the radical sign,3x+12,must be greater than or equal to 0.2.()7af xxx26.()9xbg xx.()312c h xx3x+12 03x -12x -4()312h xxThe domain of h is x|x -4 or the interval

17、-4,oo).ProblemsEvaluate each function for the given values.1.F(x)=3x+7 a.F(4)b.F(x+1)c.F(-x)2.F(x)=a.f(16)b.f(-24)c.f(25-2x)Exercises page 160,numbers 1-7 odd,21 31 odd,51 71 odd.625r Definition of the Difference QuotientThe expression is called the difference quotient.0,)()(hhxfhxfExample:Evaluatin

18、g the Difference QuotientFor ,find and simplify:a.b.Repeat for .Exercises pg 160,numbers 33-41 odd.53)(2xxxf)(hxf0,)()(hhxfhxf37)(2xxxfPiecewise-Defined FunctionsFunctions that are made up of different pieces based upon different domains are called piecewise-defined functions.Example:Piecewise-defined function)6(b.)5(a.:find,0 if 350 if 3)(If2ffxxxxxf