log以3为底[log以4为底（log以5为底a的对数）]=log以4为底[log以3为底（log以5为底b的对数）]=0log以4为底（log以5为底a的对数）=1log以3为底（log以5为底b的对数）=1log以5为底a的对数=4log以5为底b的对数=3a=5^4b=5^3a/b=5
