Diketahui deret geometri 45+15+5+.......... Tentukan S10?

U1 = 45
U2 = 15
U3 = 5

r = Un/Un-1
r = U2/U1
r = 15/45
r = 1/3
r < 1

S10 = a(1 - r^n) / 1 - r
S10 = 45 (1 - 1/3^10) / 1 - 1/3
S10 = 45 (1 - 1/3^10) / ⅔
S10 = 3/2 × 45 (1 - 1/59049)
S10 = 135/2 (59049/59049 - 1/59049)
S10 = 135/2 (59048/59049)
S10 = 135/2 × (59048/59049)
S10 = 135 (29524/59049)
S10 = 3985740/59049

*harap koreksi