tolong bantu jawab no. 8 dan 9

8. Un = n × (n + 2)
U10 = 10 × 12 = 120 lingkaran

9. [tex] \frac{405}{45} [/tex] = 9, r² = 9 r = 3

Sn = [tex] \frac{ a (r^{n} - 1)}{r - 1} [/tex]
S6 = [tex] \frac{ 5 (3^{6} - 1)}{3 - 1}[/tex]
S6 = 1.820