已知等比数列的公比是1/2,且a1+a3+a5+……+a99=60,求a1+a2+a3+……+a100_数学解答

已知等比数列的公比是1/2,且a1+a3+a5+……+a99=60,求a1+a2+a3+……+a100

人气：298 ℃　时间：2020-04-02 20:11:52

解答

设公比是q=1/2.
a2+a4+a6……+a100
=(a1*q)+(a3*q)+(a5*q)+……+(a99*q)
=(a1+a3+a5+…+a99)*q
=60×1/2
=30
a1+a2+a3+…+a99+a100
=(a1+a3+a5+…+a99)+ (a2+a4+a6……+a100)
=60+30
=90