Answer:
You can take the sum of a finite number of terms of a geometric sequence. And, for reasons you'll study in calculus, you can take the sum of an infinite geometric sequence, but only in the special circumstance that the common ratio r is between –1 and 1; that is, you have to have | r | < 1.
this is a few formulas : Sn=a1(1−rn)1−r,r≠1,
Example 3: Find the sum of the first 8 terms of the geometric series if a1=1 and r=2 .
Explanation: