A^DE=B^EF=C^DF写得不清楚
DElgA=EFlgB=DFlgC=klgA=k/(DE)lgB=k/(EF)lgc=k/(DF)lg(A*B*C)=lgA+lgB+lgC=k/(DE)+k/(EF)+k/(DF)=DEF(D+E+F)k/(DEF)=0A*B*C=1
