Diketahui barisan bilangan : 18,6,2,2/3,2/9,2/27 tentukan suku ke 8

a = 18
b = 6-18 = -12

U8 = a+(n-1)b
U8 = 18 + (8-1).(-12)
U8 = 18 + 7. (-12)
U8 = 18 + (-84)
U8 = -66

Dik:
• a = 18
• r = 6/18 = 1/3
Dit: U8 ....?
penyelesaian
Un = ar^n-1
U8 = (18)(1/3)^7
U8 = 18 x 1/2187
U8 = 2/243