解:(1)x-
![](http://thumb.1010pic.com/pic5/latex/597.png)
x=
![](http://thumb.1010pic.com/pic5/latex/5886.png)
,
![](http://thumb.1010pic.com/pic5/latex/5192.png)
x
![](http://thumb.1010pic.com/pic5/latex/179631.png)
=
![](http://thumb.1010pic.com/pic5/latex/5886.png)
![](http://thumb.1010pic.com/pic5/latex/179631.png)
,
x=1
![](http://thumb.1010pic.com/pic5/latex/847.png)
;
(2)
![](http://thumb.1010pic.com/pic5/latex/2766.png)
:
![](http://thumb.1010pic.com/pic5/latex/7.png)
=x:15,
![](http://thumb.1010pic.com/pic5/latex/7.png)
x=
![](http://thumb.1010pic.com/pic5/latex/2766.png)
×15,
![](http://thumb.1010pic.com/pic5/latex/7.png)
x
![](http://thumb.1010pic.com/pic5/latex/215101.png)
=
![](http://thumb.1010pic.com/pic5/latex/1883.png)
![](http://thumb.1010pic.com/pic5/latex/215101.png)
,
x=40;
(3)
![](http://thumb.1010pic.com/pic5/latex/5192.png)
=x:
![](http://thumb.1010pic.com/pic5/latex/14.png)
,
8x=5×
![](http://thumb.1010pic.com/pic5/latex/14.png)
,
8x÷8=3÷8,
x=0.375;
(4)12x+7×0.3=20.1,
12x+2.1-2.1=20.1-2.1,
12x÷12=18÷12,
x=1.5.
分析:(1)先化简方程,再依据等式的性质,方程两边同时除以
![](http://thumb.1010pic.com/pic5/latex/5192.png)
求解,
(2)依据比例的基本性质,两内项之积等于两外项之积,化简等式,再依据等式的性质,方程两边同时除以
![](http://thumb.1010pic.com/pic5/latex/7.png)
求解,
(3)依据比例的基本性质,两内项之积等于两外项之积,化简等式,再依据等式的性质,方程两边同时除以8求解,
(4)先化简方程,再依据等式的性质,方程两边同时减2.1,最后同时除以12求解.
点评:本题主要考查学生运用等式的性质以及比例的基本性质解方程的能力.