可用换底公式.
为便于理解,我们先换成10为底的对数哈.
log以a分之一为底的b分之一=[log (10) (1/a) ] / [log (10) (1/b) ] = [ - log (10) (a) ] / [ - log (10) (b) ] = [ log (10) (a) ] / [ log (10) (b) ]
在用换底公式换回去,[ log (10) (a) ] / [ log (10) (b) ] =log( a )(b)