2.5的x次方=1000,0.25的y次方=1000
log2.5(1000)=x
log0.25(1000)=y
1/x=log1000(2.5)
1/y=log1000(0.25)
1/x-1/y=log1000(2.5)-log1000(0.25)
=log1000(10)
=1/3