已知数列an 满足条件:A1=1,A2=r(r>0)数列{an+an+1}是公差为d的等差数,求a1+a2.+a2n-1+a2n
问题描述:
已知数列an 满足条件:A1=1,A2=r(r>0)数列{an+an+1}是公差为d的等差数,求a1+a2.+a2n-1+a2n
答
数列an 满足条件:A1=1,A2=r(r>0)数列{an+an+1}是公差为d的等差数,令bn=an+an+1即首项b1=a1+a2=1+rb3=a3+a4=b1+2d=1+r+2db5=a5+a6=b1+4d.b(2n-1)=a2n-1+a2n=1+r+(2n-2)d所以a1+a2+.+a2n-1+a2n=(a1+a2)+...+(a2n-1...