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72,5 - ( 2x + 1 ) = 630 : 9
72,5 - ( 2x + 1 ) = 70
2x + 1 = 72,5 - 70
2x + 1 = 2,5
2x = 2,5 - 1
2x = 1,5
x = 1,5 : 2
x = 0,75
72,5 - ( 2x + 1 ) = 630 : 9
72,5 - ( 2x + 1 ) = 70
( 2x + 1 ) = 72,5 - 70
( 2x + 1 ) = 2,5
2x = 2,5 - 1
2x = 1,5
x = 1,5 : 2
x = 0,75
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![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(x+184-278\right)-\left(184-278\right)=4\\\left(x+184-278\right)-\left(-94\right)=4\\ \left(x+184-278\right)+94= 4\\ \left(x+184-278\right)= 4-94\\ \left(x+184-278\right)=-90\\ x+184=-90+278\\ x+184=188\\ x=188-184\\ 4.\)
( x + 184 - 278 ) - ( 184 - 278 ) = 4
x + 184 - 278 - 184 + 278 = 4
x + 0 = 4
x = 4
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a) x.9,85=x\)
\(\Leftrightarrow x.n=x\)
Ta có: 1 số nhân với 1 số khác mà vẫn bằng chính nó
\(\Rightarrow x=0\)
\(b)\)\(x.x=\dfrac{4}{9}\)
\(x^2=\dfrac{4}{9}\)
\(4=2^2;-2^2\)
\(9=3^3;-3^3\)
\(\dfrac{4}{9}=\left(\dfrac{2}{3}\right)^2=\left(\dfrac{2}{-3}\right)^2=\left(\dfrac{-2}{-3}\right)^2=\left(\dfrac{-2}{3}\right)^2\)
Vậy x=
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![](https://rs.olm.vn/images/avt/0.png?1311)
\(x+x.\frac{1}{4}:\frac{2}{7}+x:\frac{2}{9}=255\)
\(=x+x.\left(\frac{1}{4}:\frac{2}{7}\right)+x:\frac{2}{9}=255\)
\(=x+x.\frac{7}{8}+x:\frac{2}{9}=255\)
\(=x+x.\frac{7}{8}+x.\frac{9}{2}=255\)
\(=x+x.\left(\frac{7}{8}+\frac{9}{2}\right)=255\)
\(=x+x.\frac{43}{8}=255\)
\(\Leftrightarrow x=40\)
chúc bạn học giỏi
![](https://rs.olm.vn/images/avt/0.png?1311)
b) 541 + (218 - x) = 678
218-x=678-541
218-x=137
x=181
![](https://rs.olm.vn/images/avt/0.png?1311)
255-(x+9)=184
x+9=255-184
x+9=71
x =71-9
x =62
HT
255 - (x + 9) = 184
x + 9 = 255 - 184
x + 9 = 71
x = 71 - 9
x = 62