等差数列与等比数列的首项相等,且第（2n+1）项也相等,比较它们第（n+1）项的大小.

等差数列与等比数列的首项相等,且第（2n+1）项也相等,比较它们第（n+1）项的大小.
等差数列与等比数列的首项相等,且第（2n+1）项也相等,比较它们第（n+1）项的大小.

等差数列与等比数列的首项相等,且第（2n+1）项也相等,比较它们第（n+1）项的大小.
设等差数列为an,等比数列为bn
a1=b1
a1+2nd=b1*q^2n
a1+nd-b1*q^n=(a1+b1*q^2n)/2 -b1*q^n=a1(1-q^n)²/2
当q=1时 相等
当q≠1时,若a1>0,则an+1>bn+1,若a1