Question

how can I find the root of irrational number

Answer 1

Irrational number is one which can't be expressed as a ratio of two integers.
So. If the derived number itself is irrational, wouldn't its root be too?
As suppose say x is irrational, √x will also be irrational. 
Although there are few cases that squares of irrational number turning rational. 
We know √2 is irrational. But its square becomes rational. 

Answer 2

use long division mtd