dik: U3=3 U5=27 dit: a dan r, u7, s7

Bab Barisan dan Deret
Matematika SMP Kelas IX

Geometri
1] r = (27 : 3)^1/(5 - 3)
r = 9^(1/2)
r = 3

2] a = U3 : r²
a = 3 : 3²
a = 1/3

3] U7 = U5 x r²
U7 = 27 x 3²
U7 = 243

4] Sn = a x (r^n - 1)/(r - 1)
S7 = 1/3 x ((3^7) - 1)/(3 - 1)
S7 = 1/3 x 1/2 x 2.186
S7 = 364 1/3

r = u5 / u3
= a. r pangkat 4/ a . r pangkat 2 = 27/3
r pangkat 2 = 9
r = 3
U3 = a. r pangkat 2
3 = a . 3 pangkat 2
3 = a X 9
a = 3/9 = 1/3
U7 = a. r pangkat 6
= 1/3 X 3 pangkat 6
= 1/3 X 729
= 243
s7 = 1/3 ( 3 pangkat 7 - 1)/3-1
= 1/3 ( 2187 - 1 ) / 2
= 1/3 ( 2186) / 2
= 1/3 X 1093
= 364 1/3