Bunuel wrote:

The first term of a sequence is -2 and the second term is 2. Each subsequent odd term is found by adding 2 to the previous term, and each subsequent even terms is found by multiplying the previous term by -1. What is the sum of the first 669 terms?

A. -4 B. -2 C. 0 D. 2 E. 4

Ans:B

Solution: from the statement we can find the sequence. Which is { -2,2,4,-4,-2,2,-4,4..... }

its repetitive sequence of 4 elements and sum of those four elements (first four terms) is 0

sum of 669 terms = 668+1 terms = 0 +( -2) = -2

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