(2.5)^x=(0.25)^y=1000,;
三式分别取对数;
lg(2.5)^x=lg((0.25)^y=lg1000;
xlg2.5=ylg0.25=3;
1/x=lg2.5/3;
1/y=lg0.25/3;
1/x-1/y=(lg2.5-lg0.25)/3=lg(2.5/0.25)/3=1/3