log以14为底的56 ＝log以3为底的56/log以3为底的14 =(log以3为底的7+3log以3为底的2)/(log以3为底的2+log以3为底的7) =(b+3/a)/(1/a+b) =(ab+3)/(ab+1) log以2为底的3=lg3/lg2=a log以3为底的2=lg2/lg3=1/a
