已知公差不为0得的等差数列{an}与等比数列{bn}满足:a1=b1,a3=b3,a7=b5,
问题描述:
已知公差不为0得的等差数列{an}与等比数列{bn}满足:a1=b1,a3=b3,a7=b5,
A:b11=a13
B:b11=a31
C:b11=a63
D:b63=a11
答
公差为P,公比为Qa1=b1,a3=b3---->a1+2p=a1*q^2----->2p=a1(q^2-1)a3=b3,a7=b5---->a1+6p=a1*q^4----->6p=a1(q^2-1)(q^2+1)====>3=q^2+1---->q=1.414.------>p=a1/2(不妨设p=1)则b11=64,a31=64,选B