等差数列aN的第3,7,10成等比数列,则等比数列的公比

问题描述:

等差数列aN的第3,7,10成等比数列,则等比数列的公比

a3=a7-4da10=a7+3d a7^2=(a7-4d)(a7+3d)a7^2=a7^2-da7-12d^2da7+12d^2=0d(a7+12d)=0a7=-12d或 d=0d=0时a3=a7=a10q=1q=1a7=-12d时a3=-16da10=-9da10/a7=9/12=3/4a7/a3=12/16=3/4 q=1或3/4