真數(shù)相乘=對(duì)數(shù)相加,即
log(a)(MN)=log(a)(M)+log(a)(N).
千萬(wàn)不要和指數(shù)的混淆!
你只要記：
1+1=2,即lg10+lg10=lg100.
2-1=1,即lg100-lg10=lg10.
2*1=2.即2lg10=lg100.
考試的時(shí)候?qū)懴逻@三個(gè)式子,你就可以得出對(duì)數(shù)的運(yùn)算法則了.
= = = = = = =
求(3^lg5)*(2^lg3).
令 x=(3^lg5)*(2^lg3),
則 lg x=lg(3^lg5)+lg(2^lg3)
=lg5*lg3+lg3*lg2
=lg3*(lg5+lg2)
=lg3.
因此 x=3.
= = = = = = =
每一步原因見(jiàn)對(duì)數(shù)的運(yùn)算法則.
兩邊取對(duì)數(shù)是一種解題方法.