jumlah deret geometri tak hingga 18+9+41/2+... adalah?

18 + 9 + 4 ¹/₂ + ...

S∞ = a/(1 - r)
S∞ = 18/(1 - ¹/₂)
S∞ = 18/ ¹/₂
S∞ = 18 × 2
S∞ = 36

dik: a=18
r= 9/18 =1/2
dit: s~...???
jwb: s ~= a /1- r = 18 / 1-1/2
= 18/ 1/2
= 18x2/1
= 36/1 = 36.