loga x=lgx/lga=24
logb x=lgx/lgb=40
lga=lgx/24,lgb=lgx/40
lgab=lga+lgb=lgx/15
logabc x=lgx/lgabc=12
lgabc=lgx/12
lgc=lg(abc/ab)=lgabc-lgab=lgx/60
所以logc x=lgx/lgc=lgx/(lgx/60)=60
loga x=lgx/lga=24
logb x=lgx/lgb=40
lga=lgx/24,lgb=lgx/40
lgab=lga+lgb=lgx/15
logabc x=lgx/lgabc=12
lgabc=lgx/12
lgc=lg(abc/ab)=lgabc-lgab=lgx/60
所以logc x=lgx/lgc=lgx/(lgx/60)=60