This unit has two main topics: relations and functions. In our daily life, we come across many patterns that characterize certain relations such as mother and son, teacher and student, country and continent, etc. Similarly, in mathematics, we come across different relations such as 5 > 2, 5 is a factor of 20 and formulas that relate two quantities. In this section, we will focus on mathematical relations and special type of relation which is called function.