log2 3=mlg3/lg2=mlg3=mlg2同理lg7=nlg3所以lg7=mnlg2log42 56=(lg56)/(lg42)=(lg8*7)/(lg2*3*7)=(3lg2+lg7)/(lg2+lg3+lg7)=(3lg2+mnlg2)/(lg2+mlg2+mnlg2)=(3+mn)/(1+m+mn)