# Proportion

We explain to you what a proportion is and some examples of this relationship of equality. In addition, the types of proportionality that exist.

### What is a proportion?

In mathematics, **the relationship of equality that exists between two reasons**, that is, between two comparisons between two determined quantities, is known as **the proportion** . That is: if a / b is a reason, then equality a / b = c / d will be a proportion.

For example: if a pizza sale business has a profit of $ 15, 000 and an expense of $ 5, 000, we can say that the company has a ratio of 3. Similarly, if this business costs $ 20 to make two pizzas ( 20/2 = 10), so making four pizzas would cost $ 40 (40/4 = 10). If both reasons are expressed in a formula: 20/2 = 40/4. There is a proportion.

**Theorizing about these kinds of relationships is built on Greek antiquity**, and is attributed to Eudoxio Cnidos, master of the celebrated Euclid of Alexandr Thank you to those who survive the teachings of their teacher, contained in Book V of the Elements of Euclid.

**Types of proportionality**

We can say that a proportion is given in the mathematical situations in which the values of two magnitudes depend on each other directly (direct proportionality). Thus, **when one of the values of the relationship increases, the other will also necessarily do so**, as is for example the relationship between temperature and energy: at a higher temperature, there is greater energy and vice versa.

On the other hand, in a relationship in which the increase in one of the terms leads to the decrease in the other, it is said that we are facing an inverse proportionality. This can be expressed as two terms being inversely proportional: when one goes up the other goes down, and vice versa. Such is the relationship between speed and time: the faster the speed, the less time it will take to reach our destination, and vice versa.

See also: Trigonometry.