Question

10. Cho n số a1, a2, a3, a4, a5,..., a_n và mỗi số = 1 hoặc -1. CMR S_n = a1.a2 + a2.a3 + a3.a4 + a4.a5 + a5.a6 +...+ a_n.a1 = 0 khi và chỉ khi n ⋮ 4.

Gíup mình với mình đang cần gấp!

Cảm ơn mn nhiều!

Answer 1

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Answer 2

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