Cari suku yang diminta dalam setiap barisan aritmatika? A.4,7,10,13.......suku ke20 B.5,9,13,17.......suku ke 15 Tolng dibantuuuuuu yaaaaa

Rumus barisan aritmatika:
Un = a + (n - 1) × b

1) 4, 7, 10, 13, ....
b (selisih tetap) = 3
a (suku pertama) = 4

U20
= 4 + (20 - 1) × 3
= 4 + 19 × 3
= 4 + 57
= 61

2) 5, 9, 13, 17, ....
b (selisih tetap) = 4
a (suku pertama) = 5

U15
= 5 + (15 - 1) × 4
= 5 + 14 × 4
= 5 + 56
= 61