等比数列{An}各项为正数,且log3a1+log3a2+.+log3a10=10,则a5a6+a4a7=?
问题描述:
等比数列{An}各项为正数,且log3a1+log3a2+.+log3a10=10,则a5a6+a4a7=?
答
log3a1+log3a10=log3a2log3a9=log3a3+log3a8.
log3a1a10=log3a2a9=log3a3a8.
log3a1+log3a2+.+log3a10=10
5log3a1a10=10 log3a1a10=2 a1a10=9 log3a1a10=18