Question

prove that root2+root5 is irrational

Answer 1

prove? What class is this?

Answer 2

if x is rational, then x^2 is rational (x can be expressed in the form a/b, x^2 in the form a^2/b^2)
consequently if x^2 is irrational, x cannot be rational
let x=sqrt(2)+sqrt(5)
x^2=7+sqrt(10)
sqrt(10) is irrational
therefore sqrt(2)+sqrt(5) is irrational