两个等差数列{an},{bn},a1+a2+…+anb1+b2+…+bn=7n+2n+3,则a5b5=( ) A.7213 B.7 C.378 D.6512
两个等差数列{a
n},{b
n},
=,则
=( )
A.
B. 7
C.
D.
数学人气:489 ℃时间:2019-10-11 12:10:11
优质解答
由题意可设等差数列{a
n},{b
n}的前n项和分别为S
n和T
n,
∴
=
=,
∴
=
=
=
=
=
=
故选:D
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