The symbol for irrational numbers is Q.

Irrational numbers can not be written in the form of a/b, where 'a' and 'b' are integers and 'b' is not equal to zero.

Square roots of all numbers that are not perfect squares are irrational numbers. That is, all whole numbers which do not have a whole number square root have irrational square roots. So, √2, √3 and √5 are irrational numbers.

Representing irrational numbers by a number line:

√2 is an irrational number and it can be represented on the number line as follows

Representing √2 on a number line |

- Let O be the point marked 0 on the number line.
- Let A be the point marked 1 on the number line.
- From point A, draw a perpendicular AB to the number line such that this perpendicular is equal to 1 unit length, the same as the length of one unit on the number line (= 0A)
- Now join the point B with O to get a right angled triangle OAB, which has a right angle at A.
- By Pythagorean theorem, (OA)
^{2}+ (AB)^{2}= (OB)^{2} - Since OA = 1 and AB = 1, therefore 1
^{2}+ 1^{2}= (OB)^{2} - So 1 + 1 = (OB)
^{2} - 2 = (OB)
^{2} - Taking square root on both sides, √2 = OB