Tolong yah nomer 4 dan 5:)))

U1 + U2 + U3 = 210
a + ar + ar^2 = 210...(1)
U6 + U7 + U8 = 6720
ar^5 + ar^6 + ar^7 = 6720
r^5 ( a + ar + ar^2) = 6720
r^5 (210) = 6720
r^5 = 6720/210
r^5 = 32
r^5 = 2^5
r = 2
dari (1), a + ar + ar^2 = 210
a + a.2 + a.2^2 = 210
a + 2a + 4a = 210
7a = 210
a = 210/7 = 30
jumlah 2 suku pertama,
S2 = U1 + U2
= a + ar
= 30 + 30.2
= 30 +60
= 90
Jadi jumlah 2 suku pertama = 90
5) n = 7
a = 5
U7 = 320
ar^6 = 320
5r^6 = 320
r^6 = 64
r^6 = 2^6
r = 2
Sn = a { r^n - 1)/(r - 1)
S7 = 5 { 2^7 - 1)/(2-1)
= 5 (128 -1)/1
= 5 . 127
= 635
jadi panjang kawat = 635 cm