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＝a13B：b11＝a31C：b11＝a63D：b63＝a11
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