Nếu \({\log _8}3 = p\), \({\log _3}5 = q\) thì log5 bằng

* Hướng dẫn giải

\(\begin{array}{l} \log 5 = \frac{{{{\log }_3}5}}{{{{\log }_3}10}} = \frac{{{{\log }_3}5}}{{{{\log }_3}2 + {{\log }_3}5}} = \frac{q}{{q + {{\log }_3}2}}\\ {\log _3}2 = \frac{{{{\log }_8}2}}{{{{\log }_8}3}} = \frac{{\frac{1}{3}{{\log }_2}2}}{{{{\log }_8}3}} = \frac{1}{{3p}}\\ \log 5 = \frac{q}{{q + \frac{1}{{3p}}}} = \frac{{3pq}}{{3pq + 1}} \end{array}\)