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To prove :  is an irrational number.
Solution:
Let assume that is rational.

Therefore it can be expressed in the form of , where p and q are integers and q≠0

Therefore we can write =

2√3= 5 -
⇒ √3 = 

is a rational number as p and q are integers. This contradicts the fact that √3 is irrational,
so our assumption is incorrect. Therefore is irrational.
Note: Sometimes when something needs to be proved, prove it by contradiction.
Where you are asked to prove that a number is irrational prove it by assuming that it is rational number
and then contradict it.