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**“Teach A Level Maths” Vol. 2: A2 Core Modules**

1: Functions

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**A function is a rule , which calculates values of**

for a set of values of x. e.g and are functions. is called the image of x Another Notation means is often replaced by y.

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**x x We can illustrate a function with a diagram . -1 -3 . -1 . 1.5 2 .**

. 2.1 1.5 -3 . x x -1 . 2 . A few of the possible values of x 3.2 . The rule is sometimes called a mapping.

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A bit more jargon To define a function fully, we need to know the values of x that can be used. The set of values of x for which the function is defined is called the domain. In the function any value can be substituted for x, so the domain consists of all real values of x We write R We say “ real ” values because there is a branch of mathematics which deals with numbers that are not real. stands for the set of all real numbers R means “ belongs to the set ” So, means x belongs to the set of real numbers R

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What is a real number? The real numbers include both rational numbers, such as 42 and −23/129, and irrational numbers, such as p and the 2; or, a real number can be given by an infinite decimal representation, such as , where the digits continue in some way; or, the real numbers may be thought of as points on an infinitely long number line. Real numbers measure continuous quantities such as weight, height, speed, time.

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**The range of a function is the set of values given by .**

e.g. Any value of x substituted into gives a positive ( or zero ) value. So the range of is If , the range consists of the set of y-values, so domain: x-values range: y-values Tip: To help remember which is the domain and which the range, notice that d comes before r in the alphabet and x comes before y.

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**The set of values of x for which the function is defined is called the domain.**

The range of a function is the set of values given by the rule. domain: x-values range: y-values

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**e.g. 1 Sketch the function where**

and write down its domain and range. Solution: The quickest way to sketch this quadratic function is to find its vertex by differentiating. so the vertex is

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**BUT we could have drawn the sketch for any values of x.**

So, the graph of is x domain: The x-values on the part of the graph we’ve sketched go from -5 to BUT we could have drawn the sketch for any values of x. So, we get ( x is any real number ) R BUT there are no y-values less than -5, . . . so the range is ( y is any real number greater than, or equal to, -5 )

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**) ( x f y = e.g.2 Sketch the function where .**

Hence find the domain and range of Solution: is a translation from of ) ( x f y = so the graph is: domain: x-values range: y-values ( We could write instead of y )

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Asymptotes: if a function approaches a particular x or y value then the equation of this value is called an asymptote. Notice how each value of x maps (links) to ONLY one value of y . This is the definition of a function. If each value of x maps to MORE than one value of y it is NOT a function

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**Vertical asymptote at x = 2 **

As you cannot divide by zero x – 2 0 Domain : x 2 Vertical asymptote at x = 2 The function approaches the line x = 2 but never meets it Horizontal asymptote at y = 3. The graph approaches the line y = 3 but never meets it. Range : y 3 or y<3 and y>3

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SUMMARY To define a function we need a rule and a set of values. Notation: means For , the x-values form the domain the or y-values form the range e.g. For , the domain is the range is or R

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Exercise 1. Sketch the functions where For each function write down the domain and range Solution: (a) (b) domain: R domain: R range: R range:

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**x + 3 must be greater than or equal to zero.**

We can sometimes spot the domain and range of a function without a sketch. e.g. For we notice that we can’t square root a negative number ( at least not if we want a real number answer ) so, x + 3 must be greater than or equal to zero. So, the domain is The smallest value of is zero. Other values are greater than zero. So, the range is

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**One-to-one and many-to-one functions**

Consider the following graphs and Each value of x maps to only one value of y . . . Each value of x maps to only one value of y . . . and each y is mapped from only one x. BUT many other x values map to that y.

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**One-to-one and many-to-one functions**

Consider the following graphs and is an example of a many-to-one function is an example of a one-to-one function

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**Other one-to-one functions are:**

and

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**Other many-to-one functions are:**

Here the many-to-one function is two-to-one ( except at one point ! ) This is a many-to-one function even though it is one-to-one in some parts. It’s always called many-to-one.

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**We’ve had one-to-one and many-to-one functions, so what about one-to-many?**

One-to-many relationships do exist BUT, by definition, these are not functions. e.g. is one-to-many since it gives 2 values of y for all x values greater than 1. This is not a function. Functions cannot be one-to-many. So, for a function, we are sure of the y-value for each value of x. Here we are not sure.

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Section 7.6 Functions Math in Our World. Learning Objectives Identify functions. Write functions in function notation. Evaluate functions. Find.

Section 7.6 Functions Math in Our World. Learning Objectives Identify functions. Write functions in function notation. Evaluate functions. Find.

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