Jawabanmu

Jawaban paling cerdas!
2014-05-25T21:06:49+07:00
U3 = a + (n-1)b
8 = a + (3-1)b
8 = a + 2b
U8 = a + 7b = 20 => caranya samadengan U3
sistem eliminasi, a yang di eliminasi
8 = a + 2b
20 = a + 7b
=> -12 = -5b
=> b = 12/5

-> a + 2b = 8
-> a + 2.12/5 = 8
-> a + 24/5 = 8
-> a = 8 - 24/5
-> a = 16/5

Sn = n/2 (2a + (n-1)b)
S40 = 40/2 (2.(16/5) + (40-1)12/5)
       = 20 (32/5 + 468/5)
       = 20 (500/5)
       = 20 (100)
S40 = 2000
oh bukan U8, tapi U7 itu maksudnya ?
iyaa sorry sist salah soall
langsung aja yah
sistem eliminasi
a + 6b = 20
a + 2b = 8
=> 4b = 12
b = 3

a + 2b = 8
a + 2(3) = 8
a = 2

S40 = 40/2 (2(2) + (39)3)
= 20 (4 + 117)
= 20 (121)
S40 = 2420
iya gak papa
yoi..