Can i get help with problem 12, (discrete structures) chapter 2, section 2

In Exercises 3-26, use mathematical induction to prove that the statements are true for every positive integer n. [Hint: In the algebra part of the proof, if the final expression you want has factors and you can pull those factors out early, do that instead of multiplying everything out and getting some humongous expression.] 3. 1 + 5 + 9 +++++ (4n - 3) = n(2n - 1) n(n + 1)_nin + 1)(n + 2) 4. 1 + 3 + 6+ ... + 2 6 5. 4 + 10 + 16 + ... + (n - 2) = n(3n + 1) Sn(n + 1) 6. 5 + 10 + 15 + ... + 5n = 2 7.12 + 22 + ... + m2 = n(n + 1)(2n + 1) 6 8.1 +23+ ... + 1?(n + 1)2 12 + 9.1? + 32 + ... + (2n - 1)2 = n(2n - 1)(2n + 1) 3 10.1 +2 + n(n + 1)(2n + 1)(3x + 3n - 1) 30 11.1.3 +2.4 +3.5+ ... + n(n + 2) = n(n + 1)(2n + 7) 6 a" - 1 12.1 + a + 2? + ... + an! for a # 0,a # 1 a-1 1 1 1 1 13. + +++.+ 1.2 2.3 3.4 n(n + 1) 1+1 1 1 1 1 14. + + +...+ 1.3 3.5 5.7 (2n 1) (2n + 1) 2n + 1 15.12 - 22 + 32 - 4 + ... (-1)"+"(n)(n + 1) .. + (-1)"+" = 2 16.2 + 6 + 18+ ... +2.3"-1 = 3" - 1 17.22 +42 + ... + (2n) 2n(n + 1)(2n + 1) 3 18.1.2 +2.22 + 3.2 + ... +n2" = (n 1)24 + 1 + 2 n(n + 1)(n + 2) 19.1.2 + 2-3 +3 +4 + ... + n(n + 1) = 3