若数列{an}为等比数列,且a1a2=-32/3,a2a3=-24,则a4=?
问题描述：
若数列{an}为等比数列,且a1a2=-32/3,a2a3=-24,则a4=?
答
设公比为k,则k^2=（a2a3）/（a1a2）=9/4,因此k=3/2或 -3/2a2=a1×k所以a1a2=（a1）^2 ×k= -32/3,因为（a1）^2>0,所以k= -3/2所以（a1）^2=64/9,a1=8/3或 -8/3a4=a1× k^3当a1=8/3,a4= -9当a1= -8/3,a4= 9...