a1,a2,a3,a4是各项不为零的等差数列且公差d≠0,若将此数列删去某一项得到的数列(按原来的顺序)是等比数列,则a1d的值为_.

问题描述:

a1,a2,a3,a4是各项不为零的等差数列且公差d≠0,若将此数列删去某一项得到的数列(按原来的顺序)是等比数列,则

a1
d
的值为______.

a2=a1+d  a3=a1+2d  a4=a1+3d若a1、a2、a3成等比数列,则a22=a1•a3(a1+d)2=a1(a1+2d)a12+2a1d+d2=a12+2a1dd2=0d=0 与条件d≠0矛盾若a1、a2、a4成等比数列,则a22=a1•a4(a1+d)2=a1(a1+3d)a12+2a1...