Suhartono
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
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