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# Domain

## 4.1 Composite Functions

#### Composite Functions

• A composite function is different from sum or product of functions; it is like a function acting on the result of another. If you picture functions as machines (with x as the input, and f(x) as the output), it is something like the diagram shown.

Note: Here, f(x)=3 x+2,\ g(x)=x^{2}, and x=3.

• In comparison, (f+g)(x) is more like tow machines working separately with the same input x, and their two, separate outputs are placed together and packaged.
• Just like how the processes of manufacturing has an order, so does composite functions. It is important which functions comes first, and which comes next. Using the example above where f is the first function), we write the composition of g with f (say we call it as h) as h=g \circ f (read as ‘composition of f followed by g‘). The rule of h(x) is given by

## 1.2 Describing a Set and Function

#### Describing a Set

• It is not always possible to list all the elements in a set (e.g. N, Z, Q, R as above). There is a way of describing sets that is useful for infinite sets (i.e. sets with an infinite number of elements).
• The set of all x such that ____ is denoted as \left\{x:_{-----}\right\}. For example:

i) \{x:0<,\ x<1\} is the set of real numbers strictly between 0 and 1.

ii) \{x:x\leq3\} is the set of real numbers smaller or equal to 3.

iii) \{x: x>0, x \in Q\} is the set of all positive rational numbers.

Read More »1.2 Describing a Set and Function

## 3.7 Transformations of Logarithmic Functions

#### Plotting Logarithmic Functions

Example

Say y=log_{e}{x}. Ideally, you should remember the general shape of the graph, then labelling any important points (i.e. Step 2).

Generally, the steps to plot a graph are:

1. Identify the domain and range of the function.

Read More »3.7 Transformations of Logarithmic Functions

## 3.6 Transformations of Exponential Functions

#### Plotting Exponential Functions

Example

Say y=2^{x}. Ideally, you should remember the general shape of the graph, then labelling any important points (i.e. Step 2). You should try yourself for y=0.5^{x}.

Generally, the steps to plot a graph are:

Read More »3.6 Transformations of Exponential Functions

### Circles

• The equation of a ‘standard’ circle is x^{2}+y^{2}=r^{2}.
This circle has a radius of r, and its centre is the origin (0,\ 0).

E.g. The right shows the graph of the circle with equation x^{2}+y^{2}=4.

Note: Be careful here that the radius is 2, and not 4 as it should be r^{2}=4,\ r=2.

• By definition r>0 as it signifies the radius of the circle. However, if we observe the equation, r can be negative too (the interpretation of the negative sign will involve a concept called ‘vectors’).
• As we can see, x and y both have a range of [-r,\ r].

## 1.6 Trigonometric Functions

#### Graphs of Sine and Cosine Functions

• The graph of where -\pi<x<3\pi are plotted below. Do note that it extends beyond the drawn range.
• There are a few observations we can make, and we can tie it back to what we have already learnt:

i) The graph repeats itself after an interval of 2\pi units. We say that the graph has a period of 2\pi, and hence is called a periodic function. Previously, we have learnt that \sin(x+2\pi).

## 1.4 Logarithmic Functions

#### The Logarithmic Function

• The logarithmic function with base is defined as follows:

a^{x} = b is equivalent to log_{a}{b}=x, where a \in R^{+}\setminus \left \{ 1 \right \} .

Note:a \in R^{+}\setminus \left \{ 1 \right \}‘ means that could be any positive number, excluding 1.

• The expression log_{a}{y}=x is read as: ‘the logarithm of y to the base a is equal to x’.

Example

## 1.3 Exponential Functions [Free]

#### The Exponential Function

• The exponential function is defined as follows:

y=a^x, where a \in R^+\backslash {1}.

Note:a \in R^+\backslash {1}’ means that could be any positive number, excluding 1.

Example

9=3^{2}=3 \times 3 is equivalent to log_{3}9=2.

8=16^{\frac{3}{4}}=\sqrt[4]{16^{3}}=\sqrt{\sqrt{16 \times 16 \times 16}}.

Graph & Properties

Read More »1.3 Exponential Functions [Free]

## 1.2 Power Functions

#### Introduction to Power Functions

• Power functions are functions with the form f(x)=x^{n}, where n is a rational number.
• Some examples of power functions are:

f(x)=x^{2},\ f(x)=x^{4},\ f(x)=x^{\frac{1}{4}},\ f(x)=x^{-5},\ f(x)=x^{\frac{1}{3}}

• The expression x^n is read as: ‘x to the power of n’.

## 1.1 Introduction to Graph Sketching

#### Introduction to Graph Sketching

• In this section, 3 types of functions will be introduced accordingly:

i) Power functions, y=x^n, where is a number, n\neq 0.

This will be further extended into polynomial functions, which has the general form y=a_{n} x^{n}+a_{n-1} x^{n-1}+\ldots+a_{1} x+a_{0}, where a_i are real numbers, a_n\neq 0.

ii) Exponential functions, y=a^x and also logarithm functions, y=log_ax.

iii) Trigonometric functions or circular functions, which includes y=\sin x,\ y=\cos x,\ y=\tan x and more.

Read More »1.1 Introduction to Graph Sketching