SOLUTION: What is the sum of the first 15 terms in the geometric sequence 2, 4, 8? sometimes i got 65534 and sometimes i got 65536, im doing something wrong lol

Question 88472: What is the sum of the first 15 terms in the geometric sequence 2, 4, 8?
sometimes i got 65534 and sometimes i got 65536, im doing something wrong lol
Answer by bucky(2189) (Show Source): You can put this solution on YOUR website!
The answer is 65,534
.
The sum of the terms in a geometric sequence (S) is given by the equation:
.

.
in which a is the first term, r is the ratio between terms, and n is the number of terms.
In this problem a = 2, r = 2, and n = 15. Substituting these values into the equation
leads to:
.

.
A calculator will tell you that 2^15 = 32,768. Substituting this into the equation results in:
.

.
Simplify the terms that are inside the parentheses to get:
.

.
Do the multiplication in the numerator:
.

.
and the division by -1 results in:
.

.
Hope this helps you see how to use the equation for the sum of the terms in a geometric
progression.
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