#### Answer

1. Using tables;
2. Using graphs;
3. Defining by a formula;
4. Describing with words.

#### Work Step by Step

1. A function may be defined by tabularly representing the argument $x$ and the value of the function $f(x)$
2. A function may be given by the curve in the $xy$ plane where coordinates of every point from the curve represent respectively, the argument and the value of the function: $P(x,f(x)).$
3. A function may be defined by a fomula i.e. $f(x)=ax^2+bx+c$.
4. A function may be described with words. For example, you can say, the price function is defined as: Its argument is a product.
Its value is the price of that product.