Question

Please help with geometric series

Answer 1

`C. -5.15\cdot10^(13)`

Explanation:

`Common\ ratio\ (r)=(a_(n+1))/(a_n)=(-3)\\\\Sum\ (S_n)=(a(r^n-1))/(r-1)\ \ (r\\eq1)\\\\\implies S_n=(1\ (\ (-3)^(30)-1\ ))/(-4)\\\\\implies S_n=(205891132094649-1)/(-4)\\\\\approx(206\cdot10^(12))/(-4)\\\\\approx-5.15\cdot10^(13)`