Ais an equation in the form a/b=c/d that states that two ratios are equal.

proportion

Explanation:
A proportion is used to show that two ratios are equal.
It is written as follows:


We can cross multiply the terms to get:
ad = bc

If any of the above is unknown (a,b,c or d) and we are given that they are proportional, we can simply use the above ratio, cross multiply and solve for the unknown.

Proportionality is widely used in expressing similarity between geometric figures.

Hope this helps :)