6. 已知等比数列{an}\{a_{n}\}{an}为递减数列,若a2a6=6a_{2}a_{6}=6a2a6=6,a3+a5=5a_{3}+a_{5}=5a3+a5=5,则a5a7=(\frac{a_5}{a_7}=(a7a5=( )))