Tolong jawab soal ini

u 3 = a kali r pangkat 2
1 = A dikali buka kurung satu per tiga tutup kurung pangkat dua
1 = 1 /9 x a
a=u1=9

b. U5 = ar^4
= 9 (1/3) ^4
= 9 x 1/81
= 1/9

C. S10= 9 {1- (1/3) ^10} / 1-1/3
= 9 {1-1/59049} /2/3
= 27 {59048/59049} /2
= (59048/2187) /2
= 59048/4374

D. S1 + S2
= {9 (1-1/3)} /1-1/3 + { [9 (1- (1/3) ^2)]} / 1-1/3
= (9x2/3) /2/3 + {9x (1-1/9)} /2/3
= 9 + (9x8/9) /2/3
= 9 + 8x3/2
= 9 +12
= 21