MATH1131 Calculus MATHEMATICS 1A CALCULUS
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MATH1131 Calculus
MATHEMATICS 1A CALCULUS.
Section 1:- Functions and Graphs.
1. Numbers.
we will use the following notation:
The set of natural numbers, denoted by N, consists of all the whole numbers {0)1)2).....}.
The set of integers, denoted by z, consists of all the whole numbers {...)-3)-2)-1)0)1)2)3).....}. The set of rational numbers, denoted by Q, consists of all numbers of the form where p)q
are integers and q 0.
The ancient Greeks initially thought that this was all there was (they didn,t believe in negative numbers and zero either), until they discovered that ^2 could not be written as a rational number.
Theorem: ^2 is irrational.
proof:
^2 and numbers such as π and e are examples of irrational numbers. we think of the set of all real numbers are points which lie on the real line. Giving a formal deinition of real numbers is di伍cult.
we will use the following set notation:
{① e A : P (①)} denotes the set of all elements ① of A satisfying property P. For exam- ple){① e R : -1 三 ① 三 1} denotes all the real numbers between -1 and 1 (inclusive).
A U B is the intersection of A and B and denotes all the elements that are in both A and B .
A a B is the union of A and B and denotes all the elements that are in either A or B (or both).
Q is the set which has no elements)for example {① e R : ①2 < -1} = Q.
Inequalities:
You are aware of the following facts about inequalities:
For ①,g, z e R we have
i. if ① 持 g then ① + z 持 g + z
ii. if ① 持 g and z 持 0 then ①z 持 gz and if z < 0 we have ①z < gz.
Note carefully the deinition for | ① | .
| ① | = { ① ①
① > 0
① < 0
So for example) |a - 3| is equal to a - 3 if a > 3 and -(a - 3) = 3 - a if a < 3.
Note then that | ① | < 3 means -3 < ① < 3 and that |-① | = | ① | . Also note that {① : | ① -3| < 2} represents the set of all real numbers whose distance from 3 is less that 2.
Finally note that |①g| = | ① ||g| and that | ① + g| 三 | ① | + |g| . This last result is called
the triangle inequality. You will see a complex version of this in the algebra strand of the course.
Also of importance is:
Theorem: (AM-GM inequality).
If ①) g 三 0 are real numbers then
① + g 2
(This says that the arithmetic mean of two mean.)
proof:
三^①g.
positive
real numbers exceeds their
geometric
Ex: prove that for ① 持 0, we have ① +
三 2.
Ex: suppose a,b,c are positive real numbers. prove that a2 + b2 + c2 > ab + ac + bc.
Intervals: we will use the following notation when dealing with intervals. A round bracket means we do not include the endpoint while we do when a square bracket is used. For example (3, 9] means the interval 3 < ① 三 9. Note that since ininity is NOT a real number, if we wish to represent the interval from 3 onwards we write this as [3, 钝) (never use a square bracket with ininity.). Here are some further examples:
{① e R : ① 持 3} u {① e R : ① < 5} = (3, 5)
{① e R : ① 持 3} n {① e R : ① < 5} = R
{① e R : ① 持 5} n {① e R : ① < 3} = (-钝, 3) n (5, 钝)
{① e R : ① 持 5} u {① e R : ① < 3} = Q
solving Inequalities:
These are very similar to equations except that we must careful when multiplying by an
unknown. You should be familiar with solving quadratic inequations such as Ex: Find {① : ①2 - 2① - 3 持 。}.
For more di伍cult inequalities we use the following idea.
Ex: solve x 持 1 + .
Ex: solve 参 .
Functions:
You should be familiar with the function concept from school. Roughly speaking, a function f : A 一 B is a rule or formula which associates to each element of a set A (called the domain) exactly one element from another set B (called the co-domain). For the most part, we will have A = B = R. The range of the function is the set of values b in B for which there is an a E A with f (a) = b. In less formal terms, the range consists of the output of the function.You will need to be able to ind the domain and range of basic functions.
Ex: Find the domain and range of f (从) =^1 - 从2 .
Ex: use the AM-GM inequality to ind the range of g = π2 + and sketch the graph.
Ex: Find the domain of f (π) =^cos π .
It is often di伍cult to ind the range of a function. For example, what is the range of
It is important to be able to draw the graph of a given function. In most calculus problems this is crucial.
It often helps if the function is even or odd. You will recall that f is even if f (π) = f (-π) and f is odd if f (-π) = -f (π). Even functions are symmetric about the g axis and odd functions have a central symmetry with respect to the origin.
Thus, if we can draw such a function on the positive half plane we get the rest of the picture for free.
Note that if f is odd and has 0 in its domain, then f (0) = 0.
we say that f is periodic of period T if f (x + T) = f (x) for all real x in the domain of f.
You have met the trig. functions which are periodic with period 2π .
Ex: sketch: f (x) = (x - 3)2 + 4, and f (x) = .
Ex: sketch: f (x) = x if 0 三 x < 1 and f (x + 1) = f (x) for all x .
Ex: sketch f (x) = x2 for 0 < x < 1, f is periodic of period 2 and f is even.
Floor and ceiling Functions:
Ex: sketch f (x) = x -「x].
combining Functions:
If f and g are two functions, we can add, subtract and multiply them in the obvious way. we can also divide them provided g is not zero. If the range of g equals the domain of f we compose the two functions to form f 。g which we deine to be
f 。g(x) = f (g(x)).
f 。g is called the composite function of f and g.
Ex: Find f 。g and g 。f iff (x) = x3 and g(x) =^x2 + 1.
Note that some functions cannot be deined by one simple equation. Many functions which occur in the real world are deined piecewise.
!
Ex: f (x) =〈 (
cos x
1
2
sin x
if x < 0
if x = 0
if x 持 0
conic sections:
An important class of implicitly deined functions arises from the conic sections (so called because they are obtained by slicing a cone with various planes.)
You will need to recognise these:
(i) circle x2 + g2 = T2
(ii) Ellipse a(x)2(2) + b2(g2) = 1, a, b 0.
(iii) Hyperbola a(x)2(2) - b2(g2) = 1, a, b 0.
(iv) Rectangular Hyperbola g = , a 0.
other Functions:
It is assumed that you are familiar with the basic properties of polynomial functions, rational functions, the trigonometric functions, the exponential and logarithmic functions.
Graph g = .
2023-08-21
Functions and Graphs