Question

Tolong bantu besok di kumpul pakai cara yah.
Makasih.

Answer 1

S4 = 4/2 (2a +(4-1)b ) = 17
= 4a + 6b = 17
S8 = 8/2 (2a +(8-1)b ) = 58
= 8a + 28b = 58

4a + 6b = 17 -> 8a + 12b = 34

8a + 12b = 34
8a + 28b = 58
----------------------- —
16b = 24
b = 3/2
4a + 6.3/2 = 17 -> 4a = 17 - 9 -> a = 2

A. Rumus Sn
Sn = n/2 (2a + (n-1)b)
B. U9 = a + (9-1)b = 2+12 = 14
C. S9 = S8 + U9
58 + 14 = 72
atau
S9 = 9/2 (2.2 + (9-1)3/2 )
= 9/2 (4 + 12) = 72