1: Prove or disprove: The sum of 2 irrational numbers can be rational.

2:Prove or disprove: For n >= 5, 4n < 2^n

3: Prove or disprove: That 5 divides 11^n 6 for every positive integer n.

4:Prove or disprove: 12 + 22 ++ (n1)2 + n2 = (n)(n+1)(2n+1) 6

Please write down each process as clearly and specific as possible