diketahui : S=12 A=4 dit: rasio?

Kalau S tak hingga bgini
S = a/(1-r)
12 = 4/(1-r)
12×(1-r) = 4
12 - 12r = 4
12 - 4 = 12r
8 = 12r
8/12 = r
2/3 = r