\(\dfrac{4}{3}:\dfrac{2}{5}=\dfrac{4}{3}\cdot\dfrac{5}{2}=\dfrac{20}{6}=\dfrac{10}{3}\)

\(\dfrac{1}{8}:7=\dfrac{1}{8\cdot7}=\dfrac{1}{56}\)

\(3:\dfrac{4}{5}=3\cdot\dfrac{5}{4}=\dfrac{15}{4}\)

\(\dfrac{4}{5}:3=\dfrac{4}{5\cdot3}=\dfrac{4}{15}\)

5/8 x 6 + 1/3 = 15/4 + 1/3 = 49/12

5/4- 1/3 = 15/12 - 4/12 = 11/12

a) = 15/4 + 1/3 = 49/12

b) = 5/4 - 1/3 = 11/12

5/7 + 4/9 = 73/63

4/5 - 2/3 = 2/15

9/11 + 3/8 = 105/88

16/25 - 2/5 = 6/25.

a)\(\dfrac{4}{1}+\dfrac{4}{7}=\dfrac{28}{7}+\dfrac{4}{7}=\dfrac{32}{7}\)

b)\(\dfrac{11}{3}+\dfrac{1}{1}=\dfrac{11}{3}+\dfrac{3}{3}=\dfrac{14}{3}\)

4 + 4/7 = 32/7

11/3 + 1 =14/3

\(4+\dfrac{4}{7}=\dfrac{4}{1}+\dfrac{4}{7}=\dfrac{28}{7}+\dfrac{4}{7}=\dfrac{32}{7}\)

\(\dfrac{11}{3}+1=\dfrac{11}{3}+\dfrac{3}{3}=\dfrac{14}{3}\)

3- 32/ 35

= 3/1- 32/35

= 105/35- 32/35

= 73/35

a) x + (-5) = -(-7)
x - 5 = 7
x = 7 + 5
x =12

b) x - 8 = (-10)
x = (-10) + 8
x = -2

c) 2x + 20 = -22
2x = -22 - 20
2x = (-22) + (-20)
2x = -42
x = -42 : 2
x = -21

d) -(-30) - (-x) = 13
30 + x = 13
x = 13 - 30 
x =13 + (-30)
x = -17

X CHO MK NHA

a) x+(-5)=-(-7)
x - 5 = 7
x = 7+5
x=12

b) x-8=-10
x = -10 +8
x=-2

c) 2x+20=-22
2x=-22-20
2x=-42
x=-42:2
x=-21

d) -(-30)-(-x)=13 
30 +x=13
x=13-30
x=-17
Chúc bạn học tốt!

a, x + (-5) = -(-7)

    x + (-5) = 7

    x           = 7 - (-5)

   x            = 7 + 5

  x             = 12

Vậy x = 12

b, x - 8 = -10

    x      = -10 + 8

   x       = -2

Vậy x = -2

c, 2x + 20 = -22

   2x          = -22 - 20

  2x           = -42

   x            = (-42) : 2

   x            = -21

Vậy x = -21

d, -(-30) -(-x) = 13

     30 + x       = 13

            x        = 13 - 30

           x         = -17

Vậy x =-17

Hok tốt !

x/8 : 3/5 = 5/8 

x/8          = 5/8 x 3/5

x/8           = 3/8 

x : 8         = 3/8 

         x      = 3/8 x 8 

          x      = 3

x/8 = 5/8 x 3/5

x/8 = 3/8

x    = 3

X/8: 3/5 = 5/8

X/8 = 5/8 x 3/5

X/8 = 3/8

=> X = 3

\(2\left(x-5\right)+3\left(2-3x\right)=5x+7\)

\(\Leftrightarrow2x-10+6-9x=5x+7\)

\(\Leftrightarrow\left(2x-9x\right)+\left(6-10\right)=5x+7\)

\(\Leftrightarrow-7x-4=5x+7\)

\(\Leftrightarrow-7x-5x=4+7\)

\(\Leftrightarrow-12x=11\)

\(\Leftrightarrow x=\frac{-11}{12}\)

\(3x-5\left(x-2\right)+7=4x-12\)

\(\Leftrightarrow3x-5x-10+7=4x-12\)

\(\Leftrightarrow\left(3x-5x\right)-\left(10-7\right)=4x-12\)

\(\Leftrightarrow-2x-3=4x-12\)

\(\Leftrightarrow-2x-4x=3-12\)

\(\Leftrightarrow-6x=-15\)

\(\Leftrightarrow x=\frac{-15}{-6}=\frac{5}{2}\)

\(\frac{1}{5.8}+\frac{1}{8.11}+...+\frac{1}{x\left(x+3\right)}=\frac{101}{1540}\)

\(\Leftrightarrow\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{x\left(x+3\right)}=\frac{101}{1540}.3\)

\(\Leftrightarrow\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{x}-\frac{1}{x+3}=\frac{303}{1540}\)

\(\Leftrightarrow\frac{1}{5}-\frac{1}{x+3}=\frac{303}{1540}\)

\(\Leftrightarrow\frac{5}{5\left(x+3\right)}=\frac{1}{5}-\frac{303}{1540}\)

\(\Leftrightarrow\frac{5}{5x+15}=\frac{308}{1540}-\frac{303}{1540}\)

\(\Leftrightarrow\frac{5}{5x+15}=\frac{5}{1540}\)

\(\Leftrightarrow5x+15=1540\)

\(\Leftrightarrow5x=1540-15\)

\(\Leftrightarrow5x=1525\)

\(\Leftrightarrow x=1525\div5\)

\(\Leftrightarrow x=305\)

2x + 12 = 3 * ( x - 7 )

<=> 2x + 12 = 3x - 21

<=> 2x - 3x = - 21 - 12

<=> - x = - 33