The mathematics functions can be divided into these categories:

- Linear Functions
- Polynomials
- Power Functions
- Rational Functions
- Algebraic Functions
- Trigonometric Functions
- Exponential Functions
- Logarithmic Functions
- Transcendental Functions

Where the most interesting category is the Rational Functions, of which a rational function is a ratio of two polynomials:

where P and Q are polynomials. The domain consists of all values of x such that .

The interesting thing about the Rational Functions is that the graphs of some of them look like a human face! mostly the sad face.

The function

is a rational function with domain. Its graph is shown as below.

What is more, the graph of the below function

looks like the Chinese character “冏”:

Funny! Isn’t it?