
求解释!!
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a(n) = a1 + (n-1)d,
s(n) = na1 + n(n-1)d/2.
s(2n-1)
= (2n-1)a1 + (2n-1)(2n-1-1)d/2
= (2n-1)a1 + (2n-1)(n-1)d
= (2n-1)[a1 + (n-1)d] = (2n-1)a(n).
b(n)同理
和相比,就能把2n-1约掉。
s(n) = na1 + n(n-1)d/2.
s(2n-1)
= (2n-1)a1 + (2n-1)(2n-1-1)d/2
= (2n-1)a1 + (2n-1)(n-1)d
= (2n-1)[a1 + (n-1)d] = (2n-1)a(n).
b(n)同理
和相比,就能把2n-1约掉。
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