hitunglah jumlah geometri tak hingga 18+2+...

==Jawaban==
Dik:
a = 18
r = 2/18 = 1/9

Dit:
S∞ = a/(1 - r)
S∞ = 18/(1 - 1/9)
S∞ = 18/(9/9 - 1/9)
S∞ = 18/(8/9)
S∞ = 18 x 9 / 8
S∞ = 20,25