Question

Find the sum of the finite geometric series. 4 20 100 ... 312,500 the sum of the geometric series is .

Answer 1

What is the 9th term of the geometric sequence 4, -20, 100, ... 
First term, a = 4 
common ratio, r = –20 / 4 = –5 
..... ..... ..... ..... = 100 / –20 = –5 
9th term = 4 ( –5 ) ^ ( 9 - 1 ) 
..... ...... = 4 ( –5 ) ^ 8 
..... ...... = 4 ( 390,625 ) 
..... ...... = 1,562,500