suku ke-6 dari barisan deret 54,-18,6,-2 ....

U6 = a.r^(n-1)
= a.r^(6-1)
= a.r^5
a = 54
r = -1/3
U6 = 54.-1/3^5
= 54.-1/243
= -54/243
= - 2/9