Question

等差数列{an}中,S98=137,d=1,求a2+a4+a6+a8+……+a98的值

Answer 1

S98=a1+a2+a3+----+a98=137

a2+a4+a6+----a98-(a1+a3+a5+-----+a97)

=(a2-a1)+(a4-a3)+-----+(a98-a97)

=49*1=49

设x=a2+a4+a6+----a98,y=a1+a3+a5+-----+a97

x+y=137

x-y=49

x=93

a2+a4+a6+a8+……+a98=93