对数的换底公式:一种是化为同底的对数;一种是化为常用
对数便于约分等.
例题：{log(4)3+log(8)3}{log(3)2+log(9)2}
=[(lg3/lg4)+(lg3/lg8)][(lg2/lg3)+(lg2/lg9)](用了换底公式)
=[(lg3/2lg2)+(lg3/3lg2)][(lg2/lg3)+(lg2/2lg3)]
=[(3lg3+2lg3)/(6lg2)][(2lg2+lg2)/(2lg3)]
=[(5lg3)/(6lg2)][(3lg2)/(2lg3)]
=(5/6)×(3/2)
=5/4
希望对你有所帮助