A number is irrational if there are infinite decimal places non-recurrent, therefore it cannot be expressed in the form of fraction.
The best known irrational number is , which is defined as the relationship between the perimeter of the circle and its diameter.
Other irrational numbers are:
The number e appears in growth processes, in radioactive decay and in the formula of the catenary, which is the curve that is found in power lines.
e = 2.718281828459...
The golden ratio, , used by artists from all periods (Phidias, Leonardo da Vinci, Alberto Dürer, Dalí,..) in the proportions of their works.