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 +···+ (n-1)2 + n2 = (n)(n+1)(2n+1) 6
Please write down each process as clearly and specific as possible