Question

is the number (5+ root4) (5- root4) rational or irrational

Answer 1

( 5 + root4) (5 - root 4)

= [ 5^2 - (root4)^2]

= 25 - 4

= 21

We know that 21 is a rational number.

So, The given number is also rational.

Answer 2

$(5 + \sqrt{4)} (5 - \sqrt{4)}$
(a+b)(a-b)=a²-b²
it is =(5)²-(√4)²
=25-4=21
and the 21 is rational


I hope this will help you