等差数列m是奇数a1+a3.+am=44 a2+a4+am-1=33 求m
等差数列{a}项数m是奇数a1+a3....+am=44 a2+a4+.....am-1=33 求m
人气:402 ℃ 时间:2020-05-26 12:54:08
解答
a1+a3+a5+.+am=44 (1)
a2+a4+.+am-1=33 (2)
(1)-(2) a1+[(m-1)/2]*a1=11
a1*(m+1)/2=11
(m+1)*a1=22 m为奇数
m+1为偶数,22可以分解为 11*2,22*1
因为m-1>0,m+1只能等于22
m=11 a1=2
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