1.1 Introduction
When you look in a dictionary, you can find different definitions about equations. In order to explain in the easiest possible way, you can say that an equation:
 is an equality between two mathematical expression, which are called the left hand side and the right hand side.
 Contains one or several unknowns. If it contains an unknown, we usually use the letter x.
Example:
5x + 2 =
18
The letter x is an unknown and 5x + 2 is equal to 18, it is an equality.
