Jawabanmu

2014-05-05T17:40:56+07:00
11. Un = a + (n-1)b = 3 + (n-1)4
U7 = 3 + (7-1)4 = 3 + 24 = 27
U8 = 3 + (8-1)4 = 3 + 28 = 31
jumlah suku ke7 daan ke 8 = 27 + 31 = 58 (B)

12. U4 = a + 3b = -16
U6 = a + 5b = -30
pake eliminasi ketemu 2b = -14,, b = -7 jadi a = 5
U9 = a + (n-1)b = 5 + 8x-7 = 5 + -56 = -51 (A)