tolong bantu ya kak besok dikumpulkan
Penjelasan dengan langkah-langkah:
1)
a. –½, 1, –2, ...
Un = –½ × (–2)ⁿ-¹
U9 = –½ × (–2)^(9-1)
U9 = –½ × (–2)^8
U9 = 256/–2
U9 = –128
b. S9 = –½(1 – (–2)^9)
1 – (–2)
S9 = –½(1 – (–512))
3
S9 = 1 + 512
–6
S9 = –513
6
S9 = –85½
2)
U7 = 10
U13 = –2
b = U13 – U7
13 – 7
b = –2 –10
6
b = –12
6
b = –2
U7 = a + 6b
10 = a + 6(–2)
a = 10 + 12
a = 22
3 suku pertama = 22, 20, 18
3)
U3 = 36
U1 16
ar² = 9
a 4
r² = 9
4
U5 = U3 × r²
U5 = 36 × 9
4
U5 = 324
4
