-x/21=20/7
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, \(x=-\frac{21}{20}-\frac{-7}{15}\)
\(x=\frac{-7}{12}\)
b, \(\frac{7}{2}-x=\frac{-21}{20}:\frac{5}{4}\)
\(\frac{7}{2}-x=\frac{-21}{25}\)
\(x=\frac{7}{2}-\frac{-21}{25}\)
\(x=\frac{217}{50}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: =>3/8x6/3<x<20/21x21/4
=>3/4<x<5
hay \(x\in\left\{1;2;3;4\right\}\)
b: =>56/42<x<11/2
=>4/3<x<11/2
nên \(x\in\left\{2;3;4;5\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: =>3/8x6/3<x<20/21x21/4
=>3/4<x<5
hay \(x\in\left\{1;2;3;4\right\}\)
b: =>56/42<x<11/2
=>4/3<x<11/2
nên \(x\in\left\{2;3;4;5\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{-x}{21}=\dfrac{20}{7}\)
\(\Rightarrow x=\dfrac{-\left(20.21\right)}{7}\)
\(\Rightarrow\)\(x=-60\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, 6/7*8/15*7/6*15/16
=(6/7*7/6)*(8/15*15/16)
=1*1/2
=1/2
b, Đề bài hơi sai
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
7/2 - x=-21/20:5/4
7/2 - x= -21/25
X=7/2 - (-21/25)
X=2117/50
Nha bạn
-x/21 = 20/7
7 * ( -x ) = 21 * 20
7 ( -x ) = 420
-x = 420/7 = 60
x = -60