\(a,\dfrac{-1}{8}=\dfrac{3}{x}\\ \dfrac{3}{-24}=\dfrac{3}{x}\\ x=-24\\ b,\dfrac{x}{3}=\dfrac{3}{x}\\ x.x=3.3\\ x^2=9\\ x=\pm3\\ c,\dfrac{3}{4}.x=1\dfrac{1}{2}\\ \dfrac{3}{4}.x=\dfrac{3}{2}\\ x=\dfrac{3}{2}:\dfrac{3}{4}\\ x=2\\ d,x-\dfrac{3}{10}=\dfrac{7}{15}:\dfrac{3}{5}\\ x-\dfrac{3}{10}=\dfrac{7}{9}\\ x=\dfrac{7}{9}+\dfrac{3}{10}\\ x=\dfrac{97}{90}\\ e,\dfrac{-4}{7}-x=\dfrac{-8}{3}.\dfrac{3}{7}\\ \dfrac{-4}{7}-x=\dfrac{-8}{7}\\ x=\dfrac{-4}{7}+\dfrac{8}{7}\\ x=\dfrac{4}{7}\\ \)

f: =>x*4/7=1/5+2/3=3/15+10/15=13/15

=>x=91/60

g: =>1/3:3x=1/5-2/3=-7/15

=>3x=-5/7

=>x=-5/21

h: =>7/8x=-1/9

=>x=-1/9:7/8=-1/9*8/7=-8/63

j: =>(2,8x-50)=34

=>2,8x=84

=>x=30

a) \(\dfrac{4}{7}\times x=\dfrac{5}{9}+\dfrac{1}{5}=\dfrac{34}{45}\)

\(x=\dfrac{34}{45}:\dfrac{4}{7}=\dfrac{119}{90}\)

b) \(\dfrac{11}{15}:x=\dfrac{2}{3}-\dfrac{9}{15}=\dfrac{1}{15}\)

\(x=\dfrac{11}{15}:\dfrac{1}{15}=11\)

a) 4/7 x X - 1/5 = 5/9   

     4/7 x X         = 5/9 + 1/5

     4/7 x X         =  34/45

             X          = 34/45 : 4/7

             X          =  119/90

 b)9/15 + 11/15 : X = 2/3

               11/15 : X = 2/3 - 9/15

               11/15 : X =  1/15

                           X = 11/15 : 1/5 

                           X = 11

2: 

a: =>x-1/5=2/15

=>x=2/15+3/15=5/15=1/3

b: =>x+7/12=-5/6-2/6=-7/6

=>x=-14/12-7/12=-21/12=-7/4

c: =>x+2/3=-10/3

=>x=-4

d: =>1/4:x=-11/4

=>x=-1/4:11/4=-1/11

e: =>8:x=1,6

=>x=5

Bài 2:

a: \(\Leftrightarrow x-1\in\left\{1;-1;2;-2;3;-3;6;-6\right\}\)

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

b: \(\Leftrightarrow x+3\in\left\{1;-1;3;-3;5;-5;15;-15\right\}\)

=>\(x\in\left\{-2;-4;0;-6;2;-8;12;-18\right\}\)

c: \(\Leftrightarrow x+3\in\left\{1;-1;2;-2;3;-3;4;-4;6;-6;12;-12\right\}\)

=>\(x\in\left\{-2;-4;-1;-5;0;-6;1;-7;3;-9;9;-15\right\}\)

d: =>x+1+15 chia hết cho x+1

=>\(x+1\in\left\{1;-1;3;-3;5;-5;15;-15\right\}\)

=>\(x\in\left\{0;-2;2;-4;4;-6;14;-16\right\}\)

a: x*3/4=1/5

=>x=1/5:3/4=1/5*4/3=4/15

b: x*3/7=2/5

=>x=2/5:3/7=2/5*7/3=14/15

c: 1/3+2/9=2/12x

=>1/6x=3/9+2/9=5/9

=>x=5/9*6=30/9=10/3

d: 4/15*x-2/3=1/5

=>4/15*x=2/3+1/5=10/15+3/15=13/15

=>4x=13

=>x=13/4

e: x:1/7=2/3

=>x=2/3*1/7=2/21

f: 1/9:x=7/3

=>x=1/9:7/3=1/9*3/7=3/63=1/21

j: 1/4+5/12=8/3:x

=>8/3:x=3/12+5/12=8/12=2/3

=>x=4

h: =>7/4:x=1/5+1/2=7/10

=>x=7/4:7/10=10/4=5/2

a: =>x^2-25-x^2-3x=10

=>-3x=35

=>x=-35/3

b: =>4x^2-9-4(x^2+4x+4)=5

=>4x^2-9-4x^2-16x-16-5=0

=>-16x-30=0

=>x=-15/8

c: =>9x^2+45x-9x^2+4=7

=>45x=3

=>x=1/15

d: =>x^3+3x^2+3x+1-x^3-3x^2+5x=8

=>8x=7

=>x=7/8

2/10 = 1/5

=> x = 1

3/5 x  = 1/4 + 1/3

3/5x = 7/12

x = 7/12 : 3/5

x = 35/36

1/5: x = 2/35

x = 1/5 : 2/35

x = 7/2

\(\dfrac{x}{5}=\dfrac{2}{10}\)

=> \(\dfrac{x}{5}=\dfrac{1}{5}\)

=> x=1

\(\dfrac{3}{5}x-\dfrac{1}{3}=\dfrac{1}{4}\)

=>\(\dfrac{3}{5}x=\dfrac{1}{4}+\dfrac{1}{3}\)

=>\(\dfrac{3}{5}x=\dfrac{7}{12}\)

=>   \(x=\dfrac{7}{12}:\dfrac{3}{5}\)

=>   x = \(\dfrac{35}{36}\)

\(\dfrac{1}{5}:x=\dfrac{1}{5}-\dfrac{1}{7}\)

=>\(\dfrac{1}{5}:x=\dfrac{2}{35}\)

=>        \(x=\dfrac{1}{5}:\dfrac{2}{35}\)

=>        \(x=\dfrac{7}{2}\)

\(a.x=\dfrac{5.2}{10}=1\\ b.x=\dfrac{3}{5}x=\dfrac{1}{4}+\dfrac{1}{3}=\dfrac{7}{12}\\ x=\dfrac{7}{12}:\dfrac{3}{5}=\dfrac{7}{12}.\dfrac{5}{3}=\dfrac{35}{36}\\ c.\dfrac{1}{5}:x=\dfrac{2}{35}\\ x=\dfrac{1}{5}:\dfrac{2}{35}=\dfrac{1}{5}.\dfrac{35}{2}=\dfrac{7}{2}\)

Câu 3: 
Chiều rộng là 90x3/5=54(m)

Chu vi là (90+54)x2=288(m)

Câu 4:

Chiều rộng là 60x3/5=36(m)

Chu vi là (60+36)x2=192(m)
Diện tích là 60x36=2160(m²)

C1: a) 7/15+4/5=7/15+12/15=19/15.

b) 4/5x5/8=(4x5)/(5x8)=20/40=1/2.

c) 2/3-3/8=(2x8-3x3)/(3x8)=7/24.

d) 1/2:2/5=1/2x5/2=(1x5)/(2x2)=5/4.

C2: a) x+3/4=5/3

x=5/3-3/4

x=11/12.

b) x-2/3=7/2

x=7/2+2/3

x=25/6.

C3: Chiều rộng của mảnh đất hình chữ nhật là:

90x3/5=54 (m).

Chu vi của mảnh vườn là:

2x(90+54)=288 (m).

Đáp số: 288 m.

C4: Chiều rộng sân bóng hình chữ nhật là:

60x3/5=36 (m).

Chu vi sân bóng là:

2x(60+36)=192 (m).

Diện tích sân bóng là:

60x36=2160 (m²).

Đáp số: 192 m và 2160 m².

C5: 198x27+198x72+198=198x(27+72+1)=198x100=19 800.

5 + ( x + 27 ) = 64

a) \(\Rightarrow x+27=59\Rightarrow x=32\)

b) \(\Rightarrow x-2=39\Rightarrow x=41\)

c) \(\Rightarrow x+5=-322\Rightarrow x=-327\)

d) \(\Rightarrow5x=35\Rightarrow x=7\)

e) \(\Rightarrow4\left(x-5\right)=56\Rightarrow x-5=14\Rightarrow x=19\)

f) \(\Rightarrow15+x=37\Rightarrow x=22\)

g) \(\Rightarrow7\left(13-x\right)=35\Rightarrow13-x=5\Rightarrow x=8\)

h) \(\Rightarrow10\left(x+1\right)=100\Rightarrow x+1=10\Rightarrow x=9\)

a) 5.2² + (x + 3) = 5²

5.4 + x + 3 = 25

20 + x + 3 = 25

x + 23 = 25

x = 25 - 23

x = 2

b) 2³ + (x - 3²) = 5³ - 4³

8 + (x - 9) = 125 - 64

8 + x - 9 = 61

x - 1 = 61

x = 61 + 1

x = 62

c) 4.(x - 5) - 2³ = 2⁴.3

4x - 20 - 8 = 16.3

4x - 28 = 48

4x = 48 + 28

4x = 76

x = 76 : 4

x = 19

d) 5.(x + 7) - 10 = 2³.5

5x + 35 - 10 = 8.5

5x + 25 = 40

5x = 40 - 25

5x = 15

x = 15 : 5

x = 3

e) 7² - 7.(13 - x) = 14

49 - 91 + 7x = 14

7x - 42 = 14

7x = 14 + 42

7x = 56

x = 56 : 7

x = 8

a) \(5\cdot2^2+\left(x+3\right)=5^2\)

\(\Rightarrow x+3=5^2-5\cdot2^2\)

\(\Rightarrow x+3=25-5\cdot4\)

\(\Rightarrow x+3=5\)

\(\Rightarrow x=5-3\)

\(\Rightarrow x=2\)

b) \(2^3+\left(x-3^2\right)=5^3-4^3\)

\(\Rightarrow8+\left(x-9\right)=125-64\)

\(\Rightarrow8+x-9=61\)

\(\Rightarrow x-1=61\)

\(\Rightarrow x=61+1\)

\(\Rightarrow x=62\)

c) \(4\left(x-5\right)-2^3=2^4\cdot3\)

\(\Rightarrow4\left(x-5\right)=2^4\cdot3+2^3\)

\(\Rightarrow4\cdot\left(x-5\right)=16\cdot3+8\)

\(\Rightarrow4\cdot\left(x-5\right)=56\)

\(\Rightarrow x-5=56:4\)

\(\Rightarrow x-5=14\)

\(\Rightarrow x=19\)

d) \(5\left(x+7\right)-10=2^3\cdot5\)

\(\Rightarrow5\left(x+7\right)=8\cdot5+10\)

\(\Rightarrow5\left(x+7\right)=40+10\)

\(\Rightarrow5\left(x+7\right)=50\)

\(\Rightarrow x+7=10\)

\(\Rightarrow x=10-7\)

\(\Rightarrow x=3\)

e) \(7^2-7\left(13-x\right)=14\)

\(\Rightarrow7\left(13-x\right)=7^2-14\)

\(\Rightarrow7\left(13-x\right)=49-14\)

\(\Rightarrow7\left(13-x\right)=35\)

\(\Rightarrow13-x=5\)

\(\Rightarrow x=13-5\)

\(\Rightarrow x=8\)

f) \(5x-5^2=10\)

\(\Rightarrow5x=10+5^2\)

\(\Rightarrow5x=10+25\)

\(\Rightarrow5x=35\)

\(\Rightarrow x=\dfrac{35}{5}\)

\(\Rightarrow x=7\)

g) \(9x-2\cdot3^2=3^4\)

\(\Rightarrow9x=3^4+2\cdot3^2\)

\(\Rightarrow9x=81+2\cdot9\)

\(\Rightarrow9x=99\)

\(\Rightarrow x=\dfrac{99}{9}\)

\(\Rightarrow x=11\)

h) \(10x+2^2\cdot5=10^2\)

\(\Rightarrow10x=10^2-2^2\cdot5\)

\(\Rightarrow10x=100-4\cdot5\)

\(\Rightarrow10x=80\)

\(\Rightarrow x=\dfrac{80}{10}\)

\(\Rightarrow x=8\)

i) \(125-5\left(4+x\right)=15\)

\(\Rightarrow5\left(4+x\right)=125-5\)

\(\Rightarrow5\left(4+x\right)=120\)

\(\Rightarrow4+x=\dfrac{120}{5}\)

\(\Rightarrow4+x=24\)

\(\Rightarrow x=24-4\)

\(\Rightarrow x=20\)

j) \(2^6+\left(5+x\right)=3^4\)

\(\Rightarrow5+x=3^4-2^6\)

\(\Rightarrow5+x=81-64\)

\(\Rightarrow5+x=17\)

\(\Rightarrow x=17-5\)

\(\Rightarrow x=12\)

f) 5x - 5² = 10

5x - 25 = 10

5x = 10 + 25

5x = 35

x = 35 : 5

x = 7

g) 9x - 2.3² = 3⁴

9x - 2.9 = 81

9x - 18 = 81

9x = 81 + 18

9x = 99

x = 99 : 9

x = 11

h) 10x - 2².5 = 10²

10x - 4.5 = 100

10x - 20 = 100

10x = 100 + 20

10x = 120

x = 120 : 10

x = 12

i) 125 - 5.(4 + x) = 15

5.(4 + x) = 125 - 15

5.(4 + x) = 110

4 + x = 110 : 5

4 + x = 22

X = 22 - 4

x = 18

j) 2⁶ + (5 + x) = 3⁴

64 + 5 + x = 81

69 + x = 81

x = 81 - 69

x = 12