Question

已知数列{an}、{bn}都是等差数列，Sn，Tn分别是它们的前n项和，并且SnTn＝7n+1n+3，则a2+a5+a17+a22b8+b1

已知数列{an}、{bn}都是等差数列，Sn，Tn分别是它们的前n项和，并且SnTn＝7n+1n+3，则a2+a5+a17+a22b8+b10+b12+b16=______．

Answer 1

a2+a5+a17+a22

b8+b10+b12+b16

=

(a2+a22) +(a5+a17)

(b8+b16) +(b10+b12)

=

2a12+2a11

2b12+2b11

=

a1+a22

b1+b22

=

22 2 (a1+a22)

22 2 (b1+b22)

=

S22

T22

=

7×22+1

22+3

=

31

5

．
故答案：

31

5

．