caranya gmn plis dikumpulin skrng

Bab Barisan dan Deret
Matematika SMP Kelas VIII

r = (U6 : U3)^(1/(6 - 3))
r = (486 : 18)^(1/3)
r = 27^(1/3)
r = 3

U1 = a
a = U3 : r²
a = 18 : 3²
a = 18 : 9
a = 2