a, \(\frac{2}{3}:\frac{5}{7}:\frac{x}{9}=\frac{2}{7}:\frac{3}{5}:\frac{10}{9}\Leftrightarrow\frac{2\times7\times9}{3\times5\times x}=\frac{2\times5\times9}{7\times3\times10}\Leftrightarrow\frac{42}{5\times x}=\frac{3}{7}\Leftrightarrow294=15\times x\Leftrightarrow x=19,6\)

Các phần sau tương tự.

Dùng phương pháp nhân chéo và kiểm tra trình độ tính toán, khả năng rút gọn.

Thay kết quả vào x để kiểm tra lại bài.

cho hỏi Xx9/7:3/4=12/15

\(a,\dfrac{3}{4}x-\dfrac{7}{12}=\dfrac{5}{6}-\dfrac{2}{3}\\ \Rightarrow\dfrac{3}{4}x-\dfrac{7}{12}=\dfrac{1}{6}\\ \Rightarrow\dfrac{3}{4}x=\dfrac{1}{6}+\dfrac{7}{12}\\ \Rightarrow\dfrac{3}{4}x=\dfrac{3}{4}\\ \Rightarrow x=\dfrac{3}{4}:\dfrac{3}{4}\\ \Rightarrow x=1\\ b,\dfrac{-5}{x}=\dfrac{20}{28}\\ \Rightarrow\dfrac{-5}{x}=\dfrac{5}{7}\\ \Rightarrow\dfrac{-5}{x}=\dfrac{-5}{-7}\\ \Rightarrow x=-7\\ c,2\dfrac{1}{3}:x=7\\ \Rightarrow\dfrac{7}{3}:x=7\\ \Rightarrow x=\dfrac{7}{3}:7\\ \Rightarrow x=\dfrac{1}{3}\)

\(d,\dfrac{-105}{12}< x< \dfrac{20}{7}\Rightarrow x\in\left\{-8;-7;...;2\right\}\)

a: \(\Leftrightarrow x\cdot\dfrac{3}{4}=\dfrac{3}{4}\)

hay x=1

b: \(\Leftrightarrow x=\dfrac{-28\cdot5}{20}=-7\)

c: \(\Leftrightarrow x=\dfrac{7}{3}:7=\dfrac{1}{3}\)

d: \(\Leftrightarrow-8< x< 3\)

hay \(x\in\left\{-7;-6;-5;-4;-3;-2;-1;0;1;2\right\}\)

\(a)\dfrac{3}{4}x-\dfrac{7}{12}=\dfrac{1}{6}\\ \dfrac{3}{4}x=\dfrac{1}{6}+\dfrac{7}{12}\\ \dfrac{3}{4}x=\dfrac{2}{3}\\ x=\dfrac{2}{3}:\dfrac{3}{4}\\ x=\dfrac{8}{9}\\ b)-\dfrac{5}{x}=\dfrac{20}{28}\\ -5\cdot28=x\cdot20=-140\\ x=-140:20\\ x=-7\\ c)\dfrac{7}{3}:x=7\\ x=\dfrac{7}{3}:7\\ x=\dfrac{1}{3}\)

\(\left(x.7-7\right)\left(x.12+24\right)=0\)

=> \(\orbr{\begin{cases}x.7-7=0\\x.12+24=0\end{cases}}\)

=> \(\orbr{\begin{cases}7x=7\\12x=-24\end{cases}}\)

=> \(\orbr{\begin{cases}x=1\\x=-2\end{cases}}\)

\(170-\left(4+5x\right)=101\)

=> \(4+5x=170-101\)

=> \(4+5x=69\)

=> \(5x=69-4\)

=> \(5x=65\)

=> \(x=65:5=13\)

(x.7-7).(x.12+24)=0

* x.7-7=0                                  * x.12+24=0

x.7=7                                           x.12=24

   x=7:7                                            x=24:12

   x=1                                                x=2

vạy x=1 hoặc x=2

170-(4+5x)=101

4+5x=170-101

4+5x=69

5x=69-4

5x=65

  x=65:5

  x=13

vậy x=13

250:(2x-4)=145-120

250:(2x+4)=25

2x+4=250:25

2x+4=10

2x=10+4

2x=14

  x=14:2

  x=7

vậy x=7

6.x+3.x-4.x=105

x.(6+3-4)=105

x.(9-4)=105

x.5=105

   x=105:5

   x=21

vậy x=21

1) (x.7 - 7)(x.12 + 24) = 0

(7x - 7)(12x + 24) = 0

7x - 7 = 0 hoặc 12x + 24 = 0

7x = 0 + 7          12x = 0 - 24

7x = 7                 12x = -24

x = 1                    x = -2

Vậy: x = 1 hoặc x = -2

2) 170 - (4 + 5x) = 101

170 - 4 - 5x = 101

-5x + 166 = 101

-5x = -65

x = 13

3) 250 : (2x - 4) = 145 - 120

250 : (2x - 4) = 25

125 = 25(x - 2)

125 : 25 = x - 2

5 = x - 2

5 + 2 = x

7 = x

x = 7

4) 6.x + 3.x - 4.x = 105

5.x = 105

x = 105 : 5

x = 21

\(1,\Leftrightarrow7x=42\Leftrightarrow x=6\\ 2,\Leftrightarrow36-4x=4\Leftrightarrow4x=32\Leftrightarrow x=8\\ 3,\Leftrightarrow3x=35\Leftrightarrow x=\dfrac{35}{3}\\ 4,\Leftrightarrow x-12=144\Leftrightarrow x=156\\ 5,\Leftrightarrow x-14=16\Leftrightarrow x=30\\ 6,\Leftrightarrow3x-24=\dfrac{148}{73}\Leftrightarrow3x=\dfrac{1900}{73}\Leftrightarrow x=\dfrac{1900}{219}\\ 7,\Leftrightarrow33+x=45\Leftrightarrow x=12\\ 8,Sai.đề\\ 9,\Leftrightarrow\left(x+9\right):2=39\Leftrightarrow x+9=78\Leftrightarrow x=69\\ 11,\Leftrightarrow2\left(x+7\right)=38\Leftrightarrow x+7=19\Leftrightarrow x=12\\ 13,\Leftrightarrow2\left(x-51\right)=66\Leftrightarrow x-51=33\Leftrightarrow x=84\)

\(15,\Leftrightarrow x-19=9\Leftrightarrow x=28\\ 17,\Leftrightarrow\left(x-3\right):2=48\Leftrightarrow x-3=96\Leftrightarrow x=99\\ 19,\Leftrightarrow0x=46\Leftrightarrow x\in\varnothing\\ 8,Sai.đề\\ 14,\Leftrightarrow2x=209\Leftrightarrow x=\dfrac{209}{2}\\ 16,\Leftrightarrow2x+6=157\Leftrightarrow2x=151\Leftrightarrow x=\dfrac{151}{2}\\ 18,\Leftrightarrow5\left(x+4\right)=100\Leftrightarrow x+4=20\Leftrightarrow x=16\\ 20,\Leftrightarrow\left(3x-5\right)^3=27=3^3\Leftrightarrow3x-5=3\Leftrightarrow x=\dfrac{8}{3}\)

a) \(58+7x=100\)

\(=>7x=100-58\)

\(=>7x=42\)

\(=>x=42:7\)

\(=>x=6\)

b) \(3x-7=28\)

\(=>3x=28+7\)

\(=>3x=35\)

\(=>x=35:3\)

\(=>x=\dfrac{35}{3}\)

c) \(x-56:4=16\)

\(=>x-14=16\)

\(=>x=16+14\)

\(=>x=30\)

d) \(101+\left(36-4x\right)=105\)

\(=>36-4x=105-101\)

\(=>36-4x=4\)

\(=>4x=36-4\)

\(=>4x=32\)

\(=>x=32:4\)

\(=>x=8\)

e) \(\left(x-12\right):12=12\)

\(=>x-12=12.12\)

\(=>x-12=144\)

\(=>x=144-12\)

\(=>x=132\)

f) \(\left(3x-2^4\right).7^3=2.7^4\)

\(=>3x-2^4=2.7^4:7^3\)

\(=>3x-16=2.7=14\)

\(=>3x=14+16\)

\(=>3x=30\)

\(=>x=30:3\)

\(=>x=10\)

i) \(\left(10+2x\right).4^{2011}=4^{2013}\)

\(=>10+2x=4^{2013}:4^{2011}\)

\(=>10+2x=4^2=16\)

\(=>2x=16-10\)

\(=>2x=6\)

\(=>x=6:2\)

\(=>x=3\)

\(#WendyDang\)

51/60 x 12/17 : 3/10= 51/60 x 12/17 x 10/3 = 6120/3060 = 2

5/12 : 7/4 - 25/18 : 35/6 = 5/12 x 4/7 - 25/18 x 6/35 = 5/21 - 5/21 = 0

a)\(=\dfrac{51}{60}\times\dfrac{12}{17}\times\dfrac{10}{3}=\dfrac{6120}{3060}=2\)

b)\(=\dfrac{4}{7}\times\dfrac{7}{4}-\dfrac{25}{18}\times\dfrac{6}{35}=\dfrac{5}{21}-\dfrac{5}{21}=0\)

tách ra

\(1\)) \(5-\left(10-x\right)=7\)
\(10-x=5-7\)
\(10-x=-2\)
\(x=10-\left(-2\right)\)
\(x=12\)

\(2\)) \(-32-\left(x-5\right)=0\)
\(x-5=-32-0\)
\(x-5=-32\)
\(x=-32+5\)
\(x=-27\)

1)10-x=5-7

x=10-(-2)

x=12

2)x+5=0+32

x=32-5

x=27

3) -12+2x-9+x=0

-12+(2x+x-9)=0

3x-9=0+12

3x=12+9

x=21:3

x=7

4) 15-x=1-11

x=15-(-10)

x=25

5) 4-(27+3)=x-9

4-30=x-9

-26+9=x

x=-17

a: x-56:4=16

nên x-14=16

hay x=30

b: \(101+\left(36-4x\right)=105\)

\(\Leftrightarrow36-4x=4\)

hay x=8

Vì a: x-56:4=16

    =>x-14=16

   Hay:x=30

Vì b: 

   Hay:x=8

         Vậy x={30:8}

 Nếu sai thì thui nhá,đừng chửi mình!