tìm a biết:4/5-1/a=3/10
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: =>4/7<x<23/6
hay \(x\in\left\{1;2;3\right\}\)
b: =>19/10<x<27/5
hay \(x\in\left\{2;3;4;5\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a) \(x.\dfrac{3}{4}=\dfrac{9}{14}\)
\(\Rightarrow x=\dfrac{9}{14}:\dfrac{3}{4}\)
\(\Rightarrow x=\dfrac{6}{7}\)
b) \(x:\dfrac{5}{9}=\dfrac{3}{10}\)
\(\Rightarrow x=\dfrac{3}{10}.\dfrac{5}{9}\)
\(\Rightarrow x=\dfrac{1}{6}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
4/5 + ( x : 2/3 - 1/3 ) = 9/10
( x: 2/3 - 1/3 ) = 9/10 - 4/5
x : 2/3 - 1/3 = 1/10
x : 2/3 = 1/10 + 1/3
x : 2/3 = 13/30
x = 13/30 . 2/3
x =13/45
![](https://rs.olm.vn/images/avt/0.png?1311)
a)
- a = -3 => |a| = |-3| = 3
- a = 0 => |a| = |0| = 0
- a = 7 => |a| = |7| = 7
- a = -2 => |a| = |-2| = 2
- a = 1 => |a| = |1| = 1
- a = -9 => |a| = |-9| = 9
- a = 4 => |a| = |4| = 4
b)
- \(\left|a\right|=5\Rightarrow\begin{cases}a=5\\a=-5\end{cases}\)
- \(\left|a\right|=10\Rightarrow\begin{cases}a=10\\a=-10\end{cases}\)
- \(\left|a\right|=0\Rightarrow a=0\)
- \(\left|a\right|=-6\Rightarrow a\in\varnothing\)(|a| ko thể là số âm)
- \(\left|a\right|=1\Rightarrow\begin{cases}a=1\\a=-1\end{cases}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
`x-3/5 =-4/10`
`=>x=-4/10 + 3/5`
`=>x=-4/10 + 6/10`
`=>x= 2/10`
`=>x=1/5`
`----`
`(x-1)/(-2) = -8/(x-1)`
`=> (x-1).(x-1) = (-2).(-8)`
`=> (x-1)^2 = 16`
`=> (x-1)^2 = +- 4^2`
\(\Rightarrow\left[{}\begin{matrix}x-1=4\\x-1=-4\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=4+1\\x=-4+1\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=5\\x=-3\end{matrix}\right.\)
`4/5 -1/a =3/10`
`=>1/a=4/5-3/10`
`=>1/a=8/10-3/10`
`=>1/a=1/2`
`=>a=2`
\(\dfrac{4}{5}-\dfrac{1}{a}=\dfrac{3}{10}\)
\(\dfrac{1}{a}=\dfrac{4}{5}-\dfrac{3}{10}\)
\(\dfrac{1}{a}=\dfrac{5}{10}\)
\(\dfrac{1}{a}=\dfrac{1}{2}\)
\(a=2\)