-12/27 = 3x-1/9

=> -4/9 = 3x -1/9

=> 3x - 1 = -4

3x = -4 + 1 = -3

x = -3 : 3 = -1

3-x/45 = 2/9 = 1/2y

Ta có 3-x/45 = 2/9

=> 9(3-x) = 45 . 2

=> 9(3-x) = 90

3-x = 90 : 9 = 10

x = 3 - 10 = -7

2/9 = 1/2y

=> 2(2y) = 9 . 1

=> 4y = 9

y = 9 : 4 = 9/4

Bài 6:

a)\(\left(-18\right)-\left(-3\right)-12\)

\(=\left(-18\right)+3-12\)

\(=-15-12\)

\(=-27\)

b)\(85.\left(35-27\right)-35.\left(85-27\right)\)

\(=85.35-85.27-35.85+35.27\)

\(=85.\left(35-27-35\right)+35.27\)

\(=85.\left(-27\right)+35.27\)

\(=27.\left(-85+35\right)\)

\(=27.\left(-50\right)\)

\(=-1350\)

c)\(\left(-45\right).69+31.\left(-45\right)\)

\(=\left(-45\right).\left(69+31\right)\)

\(=\left(-45\right).100\)

\(=-4500\)

Bài 7:

a)\(\left(2-x\right)+10=-14\)

\(\Rightarrow2-x=-24\)

\(\Rightarrow x=26\)

b)\(14.\left|x\right|=28\)

\(\Rightarrow\left|x\right|=2\)

\(\Rightarrow\orbr{\begin{cases}x=2\\x=-2\end{cases}}\)

c)\(31-\left(17+x\right)=55\)

\(\Rightarrow17+x=-24\)

\(\Rightarrow x=-41\)

(-18)-(-3)-12=-27

85.(35-27)-35.(85-27)=-1350

(-45).69+31.(-45)=-4500

(2-x)+10=-14

\(\Leftrightarrow\)(2-x)=-14-10

\(\Leftrightarrow\)2-x=-24

\(\Rightarrow\)x=2-(-24)

\(\Rightarrow\)x=26

14.lxl=28

\(\Leftrightarrow\)lxl=28:14

\(\Leftrightarrow\)lxl=2

\(\Rightarrow\)x=-2

Bài 1:

a: \(=\dfrac{21}{7}\cdot\dfrac{15}{45}\cdot\dfrac{9}{18}=3\cdot\dfrac{1}{3}\cdot\dfrac{1}{2}=\dfrac{1}{2}\)

b: \(=\dfrac{11}{33}\cdot\dfrac{24}{8\cdot12}\cdot\dfrac{27}{9}=\dfrac{24}{96}=\dfrac{1}{4}\)

a) (x – 45).27 = 0 ó x – 45 = 0 ó x = 45

b) 45.(2x – 4).13 = 0 ó 2x – 4 = 0 ó 2x – 4 = 0 ó 2x = 4 ó x = 2

c) (x – 3).(x – 5) = 0

Vậy tập nghiệm của phương trình là S = {3;5}

a x=45+0=45

(45-27)x=413+235

         18x       =648

          x           =648:18

          x           =36

(x – 45).27 = 0

x – 45 = 0

x = 0 + 45

x = 45

Vậy x = 45

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