rumus no 4-6 barisan geometri jawab fast

4.) 7, 28, 112, 448
a = 7
r = 28/7 = 4
Un = a × r^n - 1
= 7 × 4^n - 1

5.) 16, -4, 1, -1/4
a = 16
r = -4/16 = -1/4
Un = a × r^n - 1
= 16 × -1/4^n - 1

6.) U1 = 4
a = 4

U3 = 36
a × r^3 - 1 = 36
4 × r^2 = 36
r^2 = 36/4
r^2 = 9
r = 3

U5 = a × r^5 - 1
= 4 × 3^4
= 4 × 81
= 324

ket : ^ = pangkat