Tìm x, biết: 5 , 5 x = 13 15
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(5x-\dfrac{4}{5}=x+\dfrac{13}{15}\)
\(\Rightarrow5x-x=\dfrac{13}{15}+\dfrac{4}{5}\)
\(\Rightarrow4x=\dfrac{13}{15}+\dfrac{12}{15}\)
\(\Rightarrow4x=\dfrac{25}{15}\)
\(\Rightarrow4x=\dfrac{5}{3}\)
\(\Rightarrow x=\dfrac{5}{3}:4\)
\(\Rightarrow x=\dfrac{5}{12}\)
5x-4/5=x+13/15
<=>5x-x=13/15+4/5
<=>4x=5/3
<=>x=5/12
vậy ...
![](https://rs.olm.vn/images/avt/0.png?1311)
11/12-(5/42-x)=-(15-11/13)
=>11/13-(5/42-x)=184/13
=>5/42-x=11/13- (-184/13)
=>5/42-x=15
=>x=5/42-15
=>x=-625/42
5/42-x=11/13- [-(15-11/13)]=11/13+15-11/13
5/42-x=(11/13-11/13)+15=15
x=5/42-15=5/42-630/42
x=-625/42
Vậy x=-625/42
![](https://rs.olm.vn/images/avt/0.png?1311)
1: x=3/4-1/2=3/4-2/4=1/4
2: x-1/5=2/11
=>x=2/11+1/5=21/55
3: x-5/6=16/42-8/56
=>x-5/6=8/21-4/28=5/21
=>x=5/21+5/6=15/14
4: x/5=5/6-19/30
=>x/5=25/30-19/30=6/30=1/5
=>x=1
5: =>|x|=1/3+1/4=7/12
=>x=7/12 hoặc x=-7/12
6: x=-1/2+3/4
=>x=3/4-1/2=1/4
11: x-(-6/12)=9/48
=>x+1/2=3/16
=>x=3/16-1/2=-5/16
1)x= 1/4
2)x= 2/11+ 1/5
x= 21/55
3)x - 5/6 = 5/21
x = 5/21+5/6
x = 15/14
4)x/5 = 5/6 + -19/30
x:5 = 1/5
x = 1/5.5
x = 1
5) |x| - 1/4 = 6/18
|x| = 6/18 - 1/4
|x| =7/12
⇒x= 7/12 hoặc -7/12
6)x = -1/2 +3/4
x= 1/4
7) x/15 = 3/5 + -2/3
x:15 = -1/15
x = -1/15. 15
x = -1
8)11/8 + 13/6 = 85/x
85/24 = 85/x
⇒ x = 24
9) x - 7/8 = 13/12
x = 13/12 + 7/8
x = 47/24
10)x - -6/15 = 4/27
x = 4/27 + (-6/15)
x = -34/135
11) -(-6/12)+x = 9/48
x= 9/48 - 6/12
x = -5/16
12) x - 4/6 = 5/25 + -7/15
x -4/6 = -4/15
x = -4/15 + 4/6
x = 2/5
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{7}{5}x+\frac{13}{2}+\frac{6}{3}x=\frac{1}{15}x+\frac{17}{2}\)
=\(\frac{7}{5}x+\frac{6}{3}x-\frac{1}{15}x=\frac{17}{2}-\frac{13}{2}\)
\(\frac{10}{3}x=2\)
x=\(\frac{3}{5}\)
\(\frac{7}{5}.x+\frac{13}{2}+\frac{6}{3}.x=\frac{1}{15}.x+\frac{17}{2}\)
\(\left(\frac{7}{5}+2\right).x+\frac{13}{2}=\frac{1}{15}.x+\frac{17}{2}\)
\(\frac{17}{5}.x+\frac{13}{2}=\frac{1}{15}.x+\frac{17}{2}\)
\(\frac{17}{5}.x-\frac{1}{15}.x=\frac{17}{2}-\frac{13}{2}\)
\(\left(\frac{17}{5}-\frac{1}{15}\right)x=2\)
\(\frac{10}{3}.x=2\)
\(x=2:\frac{10}{3}\)
\(x=\frac{3}{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài làm:
a) \(\left(\frac{2x}{7}-5\right)\div\left(-8\right)=0,75\)
\(\Leftrightarrow\frac{2x}{7}-5=-6\)
\(\Leftrightarrow\frac{2x}{7}=-1\)
\(\Leftrightarrow x=-\frac{7}{2}\)
b) \(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)
\(\Leftrightarrow x+\frac{11}{13}-\frac{5}{42}=\frac{11}{13}-\frac{15}{28}\)
\(\Rightarrow x=-\frac{5}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=-\left(\frac{15}{28}-\frac{11}{13}\right)\)
\(\frac{11}{13}-\frac{5}{42}+x=-\frac{15}{28}+\frac{11}{13}\)
\(\frac{-5}{42}+x=-\frac{15}{28}+\left(\frac{11}{13}-\frac{11}{13}\right)\)
\(\frac{-5}{42}+x=-\frac{15}{28}\)
\(x=-\frac{15}{28}+\frac{5}{42}\)
\(x=-\frac{45}{84}+\frac{10}{84}\)
\(x=-\frac{35}{84}\)
Vậy \(x=-\frac{35}{84}\).
\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=\frac{113}{364}\)
\(\left(\frac{5}{42}-x\right)=\frac{11}{13}-\frac{113}{364}\)
\(\left(\frac{5}{42}-x\right)=\frac{15}{28}\)
\(x=\frac{5}{42}-\frac{15}{28}\)
\(x=-\frac{5}{12}\)
vậy \(x=-\frac{5}{12}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Tìm x , biết :
|x-2| = -3
Vô lí vì |x-2| phải lớn hơn hoặc bằng 0
=> không có giá trị x nào thỏa mãn đề bài trên .
|x-7| - 5 + 3 = 1
<=> |x-7| - 5 = -2
<=> |x-7| = 3
<=> x - 7 = 3 hoặc x - 7 = -3
<=> x = 10 hoặc x = 4
Vậy x€ { 10 ; 4 }
|x+5| - 5 = 4 - (-3)
<=> |x+5| - 5 = 7
<=> |x+5| = 7 + 5
<=> |x +5| = 12
<=> x + 5 = 12 hoặc x + 5 =-12
<=> x = 7 hoặc x = -17
Vậy x € { 7 ; -17 }