plisss d jawab tolongg bantu saya

1. Un= 2n (n+1)
a. U20 = 2.20 (20+1)
= 40.21 = 840

b. U30 = 2.30 (30+1)
= 60.31 = 1860

2. a. 3n+1
3.15+1 = 45+1 = 46

b. 1/2 n(n+1)
1/2.15(15-1) = 1 . 15 . 7 = 105
yang 1/2, 14 nya dibagi sama 2 jadinya 7

4. Un=n^2 + 2
a.U7= 7^2+2
= 49+2
=51

b.U9 = 9^2+2
= 81+2
= 83