Penjelasan dengan langkah-langkah:
NOMOR 1
-8 -2 4 10 ...
b = 6
Bagian A
Un = a + (n - 1)b
U8 = -8 + (8 - 1)6
U8 = -8 + 7 × 6
U8 = -8 + 42
U8 = 34
Bagian B
Sn = n/2 × (a + Un)
S8 = 8/2 × (-8 + U8)
S8 = 4 × (-8 + 34)
S8 = 4 × 26
S8 = 104
NOMOR 2
2 4 8 16 ...
r = 2
Bagian A
Un = ar^(n-1)
U6 = 2 × 2^(6-1)
U6 = 2 × 2⁵
U6 = 2 × 32
U6 = 64
Bagian B
Sn = (a × (r^n - 1)) / r - 1
S6 = (2 × (2⁶ - 1)) / 2 - 1
S6 = (2 × (64 - 1)) / 1
S6 = 2 × 63
S6 = 126
NOMOR 3
? ? 7 ? 12 ?
Un = a + (n - 1)b
U3 = a + (3 - 1)b
7 = a + 2b
a = 7 - 2b
Un = a + (n - 1)b
U5 = 7 - 2b + (5 - 1)b
12 = 7 - 2b + 4b
2b = 12 - 7
b = 5/2 = 2,5
a = 7 - 2b = 7 - 2(2,5) = 7 - 5 = 2
Sn = n/2 × (a + Un)
S6 = 6/2 × (2 + U6)
S6 = 3 × (2 + 14,5)
S6 = 3 × 16,5
S6 = 49,5
NOMOR 4
2000 (2000+10%) ((2000+10%)+10%) ... U7
b = 10/100 × 2000 = 20000 / 100 = 200
Un = a + (n - 1)b
U7 = 2000 + (7 - 1)200
U7 = 2000 + 1200
U7 = 3200
