log18(9)=a→2log18(3)=a,又log18(9)+log18(2)=1→log18(2)=1-a,所以log18(6)=log18(2)+log18(3)=1-a+a/2=1-a/2因为18ˆb=5,所以log18(5)=blog30(36)=log18(36)/log18(30)=2log18(6)/[log18(6)+log18(5)]=2(1-a/2)/(1-a/2+b)=(4-2a)/(2-a+b)