解:
(1)
![](http://thumb.1010pic.com/pic5/latex/183694.png)
=
![](http://thumb.1010pic.com/pic5/latex/13.png)
,
x=21×2,
x=42;
(2)6:x=9:24,
9x=6×24,
9x=144,
9x÷9=144÷9,
x=16;
(3)6:x=
![](http://thumb.1010pic.com/pic5/latex/183697.png)
,
![](http://thumb.1010pic.com/pic5/latex/21045.png)
x=6×
![](http://thumb.1010pic.com/pic5/latex/6232.png)
,
![](http://thumb.1010pic.com/pic5/latex/21045.png)
x÷
![](http://thumb.1010pic.com/pic5/latex/21045.png)
=6×
![](http://thumb.1010pic.com/pic5/latex/6232.png)
÷
![](http://thumb.1010pic.com/pic5/latex/21045.png)
,
x=6×
![](http://thumb.1010pic.com/pic5/latex/6232.png)
×
![](http://thumb.1010pic.com/pic5/latex/12579.png)
,
x=10;
(4)6:9=
![](http://thumb.1010pic.com/pic5/latex/8.png)
:x
6x=9×
![](http://thumb.1010pic.com/pic5/latex/8.png)
,
6x=3,
6x÷6=3÷6,
x=
![](http://thumb.1010pic.com/pic5/latex/13.png)
;
(5)
![](http://thumb.1010pic.com/pic5/latex/15509.png)
=
![](http://thumb.1010pic.com/pic5/latex/180683.png)
,
8x=21×0.4,
8x=8.4,
8x÷8=8.4÷8,
x=1.05;
(6)
![](http://thumb.1010pic.com/pic5/latex/168.png)
:
![](http://thumb.1010pic.com/pic5/latex/155.png)
=x:9,
![](http://thumb.1010pic.com/pic5/latex/155.png)
x=
![](http://thumb.1010pic.com/pic5/latex/168.png)
×9,
![](http://thumb.1010pic.com/pic5/latex/155.png)
x=6,
![](http://thumb.1010pic.com/pic5/latex/155.png)
x÷
![](http://thumb.1010pic.com/pic5/latex/155.png)
=6÷
![](http://thumb.1010pic.com/pic5/latex/155.png)
,
x=
![](http://thumb.1010pic.com/pic5/latex/18969.png)
.
分析:(1)根据比例的基本性质,两内项之积等于两外项之积,把原式改写成x=21×2,然后再进一步解答即可;
(2)根据比例的基本性质,两内项之积等于两外项之积,把原式改写成9x=6×24,然后等式的两边同时除以9即可;
(3)根据比例的基本性质,两内项之积等于两外项之积,把原式改写成
![](http://thumb.1010pic.com/pic5/latex/21045.png)
x=6×
![](http://thumb.1010pic.com/pic5/latex/6232.png)
,然后等式的两边同时除以
![](http://thumb.1010pic.com/pic5/latex/21045.png)
即可;
(4)根据比例的基本性质,两内项之积等于两外项之积,把原式改写成6x=9×
![](http://thumb.1010pic.com/pic5/latex/8.png)
,然后等式的两边同时除以6即可;
(5)根据比例的基本性质,两内项之积等于两外项之积,把原式改写成8x=21×0.4,然后等式的两边同时除以8即可;
(6)根据比例的基本性质,两内项之积等于两外项之积,把原式改写成
![](http://thumb.1010pic.com/pic5/latex/155.png)
x=
![](http://thumb.1010pic.com/pic5/latex/168.png)
×9,然后等式的两边同时除以
![](http://thumb.1010pic.com/pic5/latex/155.png)
即可.
点评:本题主要考查解比例,根据比例的基本性质和等式的性质进行解答即可.