设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=

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设sn是等差数列an的前n项和a6/a3=10/7则s11/s5=设sn是等差数列an的前n项和a6/a3=10/7则s11/s5=设sn是等差数列an的前n项和a6/a3=10/7则s11/s5=a

设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=
设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=

设sn是等差数列an的前n项和 a6/a3=10/7 则s11/s5=
a(n) = a + (n-1)d,
s(n) = na + n(n-1)d/2.
s(2n-1) = (2n-1)a + (2n-1)(n-1)d = (2n-1)[a + (n-1)d] = (2n-1)a(n),
s(11)/s(5) = 11a(6)/[5a(3)] = (11/5)[a(6)/a(3)] = (11/5)(10/7) = 22/7

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