Tentukan 3 suku berikutnya.dan jumlah 20 suku pertama 1. 2 5 8 11 b). 8 6 4 2 c). -8 -6 -4 -2 pakai caranya

Yang ditanyakan adalah suku ke 7.
a). 2, 5, 8, 11, 14, 17, [20]
Karena Un = a + (n - 1)b
U7 = 2 + (7 - 1)3
U7 = 2 + 6 × 3
U7 = 2 + 18
U7 = 20

Sn = n/2{2a + (n - 1)b}
S20 = 20/2 (4 + 19 × 3)
S20 = 10 (4 + 57) = 10 × 61 = 610


b). U7 = 8 + 6 × (-2)
U7 = 8 + (-12)
U7 = -4

S20 = 20/2{16 + 19 × (-2)} = 10(16 + (-38))
= 10(-22) = -220

c). U7 = -8 + 6 × 2 = -8 + 12 = 4

S20 = 20/2(-16 + 19 × 2) = 10 × (-16 + 38) =
10 × 22 = 220