suku ketiga dan suku kelima deret geometri berturut turut 32 dan 8. tentukan jumlah suku ke-4 dan jumlah suku tak hingganya

U3 = ar^2 =32 => a = 32/r^2
U5 = ar^4 = 8 =>a = 8/r^4

a = a
32/r^2 = 8/r^4
r^4/r^2 = 8/32
r^2 = 1/4
r = 1/2

a = 32/r^2 = 32÷ 1/4 = 128

S4 = 128(1 - 1/2^4) ÷ (1 - 1/2)
S4 = 128 (15/16) ÷ 1/2
S4 = 240

Stakhingga = 128/(1-1/2) = 128 ÷ 1/2 = 256