1) Ta có: \(\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{7}{25}\cdot\dfrac{5}{7}\right)\)

\(=\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{1}{5}\right)\)

=0

2) Ta có: \(\dfrac{8}{17}\cdot\dfrac{4}{15}+\dfrac{8}{17}\cdot\dfrac{22}{15}-\dfrac{8}{15}\cdot\dfrac{9}{17}\)

\(=\dfrac{8}{17}\left(\dfrac{4}{15}+\dfrac{22}{15}-\dfrac{9}{15}\right)\)

\(=\dfrac{8}{17}\cdot\dfrac{15}{15}=\dfrac{8}{17}\)

3) Ta có: \(\dfrac{2021}{2}\cdot\dfrac{1}{3}+\dfrac{4042}{4}\cdot\dfrac{1}{5}+\dfrac{6063}{3}\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\left(\dfrac{1}{3}+\dfrac{1}{5}\right)+2021\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{8}{15}+\dfrac{2021}{2}\cdot\dfrac{44}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{52}{15}\)

\(=\dfrac{52546}{15}\)

4) Ta có: \(\dfrac{4}{7}\cdot\dfrac{2}{13}+\dfrac{8}{13}:\dfrac{7}{4}+\dfrac{4}{7}:\dfrac{13}{2}+\dfrac{4}{7}\cdot\dfrac{1}{13}\)

\(=\dfrac{4}{7}\left(\dfrac{2}{13}+\dfrac{8}{13}+\dfrac{2}{13}+\dfrac{1}{13}\right)\)

\(=\dfrac{4}{7}\)

1) Tính biểu thức:

\(a\dfrac{3\times8\times7}{7\times11\times3}=\dfrac{8}{11}\)

\(b\dfrac{4}{15}\times\left(\dfrac{3}{8}+\dfrac{5}{8}\right)=\dfrac{4}{15}\times1=\dfrac{4}{15}\)

a)8/11

b) (3/8+5/8) x 4/15= 1 x 4/15= 4/15

Ta tính nhẩm như sau:

3x4=12     2x5=10    5x3=15     4x2=8

12:3=4      10:2=5    15:3=5      8:2=4

12:4=3      10:5=2     15:5=3     8:4=2

3x4 = 12               2x5 = 10        5x3 = 15                  4x2 =8

12 : 3 = 4              10 : 2 = 5       15 : 3 = 5                8 : 2 = 4

12 : 4 =3               10 :5 = 2        15 : 5 = 3                8 : 4 = 2

1: x=3/4-1/2=3/4-2/4=1/4

2: x-1/5=2/11

=>x=2/11+1/5=21/55

3: x-5/6=16/42-8/56

=>x-5/6=8/21-4/28=5/21

=>x=5/21+5/6=15/14

4: x/5=5/6-19/30

=>x/5=25/30-19/30=6/30=1/5

=>x=1

5: =>|x|=1/3+1/4=7/12

=>x=7/12 hoặc x=-7/12

6: x=-1/2+3/4

=>x=3/4-1/2=1/4

11: x-(-6/12)=9/48

=>x+1/2=3/16

=>x=3/16-1/2=-5/16

1)x= 1/4

2)x= 2/11+ 1/5

   x= 21/55

3)x - 5/6 = 5/21

   x         = 5/21+5/6

   x         = 15/14

4)x/5 = 5/6 + -19/30

   x:5 = 1/5

   x    = 1/5.5

   x    = 1

5) |x| - 1/4 = 6/18

    |x|           = 6/18 - 1/4

    |x|            =7/12

⇒x= 7/12 hoặc -7/12

6)x = -1/2 +3/4

   x= 1/4

7) x/15 = 3/5 + -2/3

   x:15  = -1/15

  x        = -1/15. 15

  x        = -1

8)11/8 + 13/6 = 85/x  

       85/24      = 85/x

  ⇒      x           = 24

9) x - 7/8 = 13/12

   x          = 13/12 + 7/8

   x          = 47/24

10)x - -6/15 = 4/27  

     x            = 4/27 + (-6/15)

    x             = -34/135

11) -(-6/12)+x = 9/48

                    x= 9/48 - 6/12

                    x = -5/16

12) x - 4/6 = 5/25 + -7/15

      x -4/6  =  -4/15

     x           = -4/15 + 4/6

    x             = 2/5

Dung vay 

a)15/8+3/4-5/12

=45+18-10/24

=53/24

b)11/24.12/33+5/6

=11.12/12.2.11.3+5/6

=1/6+5/6

=6/6=1

c)15/8+7/24:5/8

=15/8+7/24.8/5

=15/8+7.8/3.8.5

=15/8+7/15

=đề sai, nếu đúng thì như này

=8/15+7/15

=15/15=1

hbhvgvvggvgbhhgvbnj

a: \(\dfrac{5}{3}\cdot\dfrac{7}{10}=\dfrac{5}{10}\cdot\dfrac{7}{3}=\dfrac{14}{3}>2\)

\(\dfrac{5}{7}:\dfrac{7}{10}=\dfrac{5}{7}\cdot\dfrac{10}{7}=\dfrac{50}{49}< 2\)

=>\(\dfrac{5}{3}\cdot\dfrac{7}{10}>\dfrac{5}{7}:\dfrac{7}{10}\)

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

\(\dfrac{8}{9}:\dfrac{4}{3}=\dfrac{8}{9}\cdot\dfrac{3}{4}=\dfrac{8}{4}\cdot\dfrac{3}{9}=\dfrac{2}{3}\)

Do đó: \(\dfrac{4}{5}\cdot\dfrac{5}{6}=\dfrac{8}{9}:\dfrac{4}{3}\)

c: \(\dfrac{5}{11}\cdot\dfrac{33}{15}=\dfrac{5}{15}\cdot\dfrac{33}{11}=\dfrac{3}{3}=1\)

\(\dfrac{6}{17}\cdot\dfrac{34}{25}=\dfrac{34}{17}\cdot\dfrac{6}{25}=2\cdot\dfrac{6}{25}=\dfrac{12}{25}< 1\)

=>\(\dfrac{5}{11}\cdot\dfrac{33}{15}>\dfrac{6}{17}\cdot\dfrac{34}{25}\)

d: \(\dfrac{15}{19}\cdot\dfrac{38}{5}=\dfrac{15}{5}\cdot\dfrac{38}{19}=3\cdot2=6\)

\(\dfrac{15}{16}:\dfrac{3}{8}=\dfrac{15}{16}\cdot\dfrac{8}{3}=\dfrac{15}{3}\cdot\dfrac{8}{16}=\dfrac{5}{2}\)<6

=>\(\dfrac{15}{19}\cdot\dfrac{38}{5}>\dfrac{15}{16}:\dfrac{3}{8}\)

a) x* 1/5 - x* 2 * 2/15 = 4

   x * 1/5 - x * 2 = 4 : 2/15

   x * 15 - x * 2 = 30

   x * ( 15 - 2 ) = 30

   x * 13 = 30

        x = 30 : 13

        x = 30/13

 b) ( x + x * 2 ) - 3 : 1/2 = 8

     ( x * 1 + x * 2 ) - 3 = 8 x 1/2

     ( x * 1 + x * 2 ) - 3 = 4

       x * 1 + x * 2 = 4 + 3 

       x * 1 + x * 2 = 7

       x * ( 1 + 2 ) = 7

       x * 3 = 7

            x = 7 : 3

            x = 7/3

c)5 +( x * 1/2 - 4 ) = 15

    x * 1/2 - 4 = 15 - 5

    x * 1/2 - 4 = 10

    x * 1/2 = 10 + 4

    x * 1/2 = 14

          x = 14 : 1/2 

          x = 7

a)x*1/5-x*2*2/15=4

x*1/5-x*4/15=4

x*1/5-4/15=4

x*(-1/15)=4

x=4:-1/15

x=-60

15 × (4 - 7) - 15 × (5 - 3)

= 15 × (-3) - 15 × 2

= 15 × (-3 - 2)

= -15 × 5 

= -75

--------

73 × (8 - 59) - 59 × (8 - 73)

= 73 × 8 - 73 × 59 - 59 × 8 + 59 × 73

= 8 × (73 - 59) + 73 × (59 - 59)

= 8 × 14 + 73 × 0

= 8 × 14

= 112

15 x (4-7) - 15 x (5-3)

= 15 x (-3) - 15 x (-2)

= 15 x (-3 - (-2))

= 15 x (-1)

= -15

73 x (8-59) - 59 x (8-73)

= 73 x 8 - 59 x 73 - 59 x (-65)

= 73 x 8 - 59 x (73 - (-65))

= 73 x 8 - 59 x 8

= 8 x (73-59)

= 8 x 14

= 112

a) 15 × (4 - 7) - 15 × (5 - 3)

= 15 × (-3) - 15 × 2

= 15 × (-3 - 2)

= -15 × 5 

= -75

b) 73 × (8 - 59) - 59 × (8 - 73)

= 73 × 8 - 73 × 59 - 59 × 8 + 59 × 73

= 8 × (73 - 59) + 73 × (59 - 59)

= 8 × 14 + 73 × 0

= 8 × 14

= 112

1 ) l x l = 5 => x thuộc { -5 ; 5 }

Vậy x thuộc { - 5 ; 5 Ư]

2 ) l x l = 5 + 7 - 10

    l x l  = 2 => x thuộc { - 2 ; 2 }

Vậy x thuộc { - 2 ; 2 }

3 ) l x l = - 5 - l - 10 l + 15

     l x l = - 5 - 10 + 15

     l x l = 0 => x = 0

Vậy x = 0

4 ) l x l = - ( - 12 ) + ( - 15 ) + 8

     l x l = 12 + ( - 15 ) + 8

     l x l = - 3 + 8

     l x l = 5 => x thuộc { -5 ; 5 }

Vậy x thuộc { - 5 ; 5 }

1)!x!=5

=>x=5 hay x=-5

Vậy x=5 hay x=-5

Các câu khác thì tương tự nên bạn tự làm nhé!