[解析] =
==,故选A.
二、填空题
5.lg+lg的值是__1__.
[解析] lg+lg=lg(×)=lg10=1.
6.log63=0.613 1,log6x=0.386 9,则x=__2__.
[解析] log6x=0.386 9=1-0.613 1=1-log63
=log66-log63=log6=log62,∴x=2.
三、解答题
7.计算下列各式的值:
(1)lg-lg+lg;
(2).
[解析] (1)原式=(5lg2-2lg7)-×lg2+(2lg7+lg5)=lg2-lg7-2lg2+lg7+lg5=(lg2+lg5)=.
(2)原式===.
8.计算下列各式的值:
(1)log2+log212-log242;
(2)lg52+lg8+lg5·lg20+(lg2)2.
[解析] (1)原式=log2+log212-log2
=log2
=log2