Prove that is irrational.
Now, let us assume that 2√7 / 7 is a rational number
⇒ 2√7/7 = p/q (where, p & q are integers, q not equal to 0)
⇒ 2√7 = 7p/q
⇒ √7 = 7p/2q
Here, LHS is an irrational number whereas RHS is a rational number.
So by contradiction 2√7 / 7 is an irrational number