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Official 2016 Paper 1 · Q4

Paper 1Sequences & series

The sequence ana_n is defined by the rule:

an=(−1)n−(−1)n−1+(−1)n+2for n≥1.a_n=(-1)^n-(-1)^{n-1}+(-1)^{n+2}\quad\text{for }n\ge1.

Find the value of

∑n=139an\sum_{n=1}^{39}a_n
A−39-39
B−3-3
C−1-1
D0
E1
F3
G39

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