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What is the sum of the first five terms of the geometric series 3 − 6 + 12 − . . . ?

1 Answer

6 votes

Answer:

33

Explanation:

The nth term of a geometric sequence is expressed as;

Sn = a(r^n - 1)/r - 1

a is the first term of the sequence

r is the common ratio

n is the number of terms

From the sequence;

a = 3

r = -6/3 = 12/-6 = -2

n = 5 (since are looking for the sum of first five terms)

Substitute into the formula;

S5 = 3((-2)^5 - 1)/-2 - 1

S5 = 3(-32-1)/-3

S5 = 3(-33)/-3

S5 = -(-33)

S5 = 33

Hence the sum of the first five terms of the sequence is 33

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