设数列{an},{bn}都是等差数列,若a1+b1=7,a3+b3=21,则a5+b5=______.-数学

题目简介

设数列{an},{bn}都是等差数列,若a1+b1=7,a3+b3=21,则a5+b5=______.-数学

题目详情

设数列{an},{bn}都是等差数列,若a1+b1=7,a3+b3=21,则a5+b5=______.
题型:填空题难度:中档来源:江西

答案

∵数列{an},{bn}都是等差数列,
∴设数列{an}的公差为d1,设数列{bn}的公差为d2,
∴a3+b3=a1+b1+2(d1+d2)=21,
而a1+b1=7,可得2(d1+d2)=21-7=14.
∴a5+b5=a3+b3+2(d1+d2)=21+14=35
故答案为:35

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