对于等差(比)数列{an},我们可得如下性质:定理1设等差数列{an}的公差为d,前n项的和为Sn,则Sm+n=Sm+Sn+mnd(1)证在等差数列{an}中,am+k=ak+md(m,k∈N+).Sm+n=a1+a2+a3+…+am+am+1+am+2+…+am+n=Sm+(a1+md)+(a2+md)+…+(an+md)=Sm+Sn+mnd.定理2设等比数列{an}的公比为q,前n项的和 We can get the following properties for the sequence {an}: Theorem 1 Let the tolerance of the arithmetic sequence {an} be d and the sum of the first n terms be Sn, Sm + n = Sm + Sn + mnd A + a + a + a2 + a3 + ... + am + am + 1 + am + 2 + ... + k + Theorem 2 Let the geometric ratio of the equal number sequence {an} be q, and the first n items of the formula (a + md) + a2 + md + with