已知log18 9=a,18^b=5用a,b表示log30 36

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log18(9)=a
lg9/lg18=a
2lg3/(2lg3+lg2)=a
2lg3=2alg3+alg2
(2-2a)lg3=alg2
lg3=alg2/(2-2a)
18^b=5
log18(5)=b
lg5/lg18=b
lg5/(2lg3+lg2)=b
lg5=2blg3+blg2
因为lg3=alg2/(2-2a)
所以lg5=blg2/(1-a)
log30(36)
=lg36/lg30
=(2lg3+2lg2)/(lg5+lg2+lg3)
把lg3=alg2/(2-2a)
lg5=blg2/(1-a)代入并整理
log30(36)
=(4-2a)/(2b+2-a)