tentukan jumlah 15 suku pertama deret geometri diatas

a)
a = 1
r = 0,1/1 = 0,1
S15 = 1 x ( 1 - 0,1^15)/(1-0,1)
= 1 x (1 - 0,000000000000001)/(0,9)
= 10/9 x 0,99999999999999
= 1,1111111111111

b)