Jawabanmu

2014-03-27T12:33:29+07:00
Isinya 36
Sn= n(2a+(n-1)b)
       2
S8=8(2.1+(8-1)1)
      2
S8=36
2014-03-27T12:39:11+07:00
U3 = a + (3-1)b = a + 2b = 23
U8 = a + (8-1)b = a + 7b = 8
Proses eliminasi ===> -5b = 15 ===> b = -3

U8 = a + (7x-3) = 8
a = 8 - (-21)
a = 29

S8 = 8 : 2 x (2x29+(8-1)-3)
S8 = 4 x (58 + 7x(-3))
S8 = 4 x (58 - 21)
S8 = 4 x 37
S8 = 148

semoga membantu ^^
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