Jawabanmu

Jawaban paling cerdas!
2014-06-03T08:57:15+07:00
A + ar + ar² = 210
ar^5 + ar^6 + ar^7 = 6720
diperoleh
ar^5 + ar^6 + ar^7 = 6720
r^5(a + ar + ar²) = 6720
r^5(210) = 6720
r^5 = 32
r = 2
diperoleh:
a + ar + ar² = 210
a + 2a + 4a = 210
7a = 210
a = 30
U1 = a = 30
U2 = ar = 60
Jumlah dua suku pertama = 90
jawaban: E
1 5 1