3: 

\(=\dfrac{1}{7}\cdot\dfrac{3}{5}\cdot\dfrac{5}{6}\cdot\dfrac{5}{8}=\dfrac{1}{7}\cdot\dfrac{1}{2}\cdot\dfrac{5}{8}=\dfrac{5}{112}\)

4:

=>2/3:x=-2-1/3=-7/3

=>x=-2/3:7/3=-2/7

5:

AC=CB=12/2=6cm

IB=6/2=3cm

x^2=16

Suy ra x^2=4^2

Vậy x^2=4^2

[1/(x+2)-1/(x+5)]+[1/(x+5)-1/(x+10)]+[1/(x+10)-1/(x+17)]=x/15.[1/(x+2)-1/(x+17)]
1/(x+2)-1/(x+17)=x/15.[1/(x+2)-1/(x+17)]
1=x/15
x=15

sdsdxc

 720 : ( x . 2 + x . 3 ) = 3.2
720 : ( x . 2 + x.3 ) = 6
( x .2 + x.3 )           = 720 : 6 
x.2+x.3 = 120
x . ( 2 + 3 ) = 120
x . 5 = 120
     x     = 120 : 5 
    x      = 24

Bài 1:

a) \(\dfrac{9}{20}-\dfrac{8}{15}\times\dfrac{5}{12}\)

\(=\dfrac{9}{20}-\dfrac{2}{9}\)

\(=\dfrac{41}{180}\)

b) \(\dfrac{2}{3}\div\dfrac{4}{5}\div\dfrac{7}{12}\)

\(=\dfrac{2}{3}\times\dfrac{5}{4}\times\dfrac{12}{7}\)

\(=\dfrac{5}{6}\times\dfrac{12}{7}\)

\(=\dfrac{10}{7}\)

c) \(\dfrac{7}{9}\times\dfrac{1}{3}+\dfrac{7}{9}\times\dfrac{2}{3}\)

\(=\dfrac{7}{9}\times\left(\dfrac{1}{3}+\dfrac{2}{3}\right)\)

\(=\dfrac{7}{9}\times1\)

\(=\dfrac{7}{9}\)

Bài 2:

a) \(2\times\left(x-1\right)=4026\)

\(\left(x-1\right)=4026\div2\)

\(x-1=2013\)

\(x=2014\)

Vậy: \(x=2014\)

b) \(x\times3,7+6,3\times x=320\)

\(x\times\left(3,7+6,3\right)=320\)

\(x\times10=320\)

\(x=320\div10\)

\(x=32\)

Vậy: \(x=32\)

c) \(0,25\times3< 3< 1,02\)

\(\Leftrightarrow0,75< 3< 1,02\) ( S )

=> \(0,75< 1,02< 3\)

\(a,x+21=6\\ \Rightarrow x=-15\\ b,x-10=-8\\ \Rightarrow x=2\\ c,\left(-8\right)x=\left(-7\right)\left(-6\right)\\ \Rightarrow\left(-8\right)x=42\\ \Rightarrow x=-4\\ d,20+8\left(x+3\right)=5^2.4\\ \Rightarrow20+8\left(x+3\right)=25.4\\ \Rightarrow20+8\left(x+3\right)=100\\ \Rightarrow8\left(x+3\right)=80\\ \Rightarrow x+3=10\\ \Rightarrow x=7\)

\(a.x+21=6\\ x=6-21\\ x=-15\\ b.x-10=-8\\ x=-8+10\\ x=2\\ c.-8x=-7.\left(-6\right)-2\\ -8x=42-2\\ -8x=40\\ x=40:\left(-8\right)\\ x=-5\)

\(d.20+8\left(x+3\right)=5^2.4\\ 20+8x+24=25.4\\ 44+8x=100\\ 8x=100-44\\ 8x=56\\ x=56:8\\ x=7\)

a)x+21=6                    b)x-10=-8

         X=6-21                         x=-8+10

          X=-15                           x=2

C)(-8).x=-7×(-6)-2             d)20+8.(x+3)=5^2.4

     (-8).x=40                             20+8.(x+3)=100

             X=40÷8                        8.(x+3)=100-20

              X=5                               8.(x+3)=80

                                                     X+3=80÷8

                                                     X+3=10

                                                           X=10-3=7

`@` `\text {Ans}`

`\downarrow`

`a,`

`(x-1954) \times 5=50`

`x-1954 = 50 \div 5`

`x-1954 = 10`

`x=10 + 1954`

`x= 1964`

`B.`

`48 - 40 \times x=8`

`40 \times x=48-8`

`40 \times x = 40`

` x=40 \div 40`

`x=1`

`C.`

`2+70 \div x = 3`

`70 \div x = 3-2`

`70 \div x = 1`

`x=70 \div 1`

`x=70`

`D. [3 \times (x+2) \div 7]  \times  4=120`

`3 \times (x+2) \div 7 = 120 \div 4`

`3 \times (x+2) \div 7 =30`

`3 \times (x+2) = 30 \times 7`

`3 \times (x+2)=210`

`x+2=210 \div 3`

`x+2=70`

`x=70-2`

`x=68`

`E.`

`7,2 \div [ (0,6 \times x+8) \div 20 + 59] = 0,12?` Thiếu ngoặc bạn nhé._.

\(a,\left(x-1954\right)\times5=50\\ x-1954=50:5\\ x-1954=10\\ x=1954+10\\ x=1964\\b.48-40\times x=8\\40\times x=48-8\\40\times x=40\\ x=40:40\\ x=1 \\ c.2+70:X=3\\ 70:x=3-2\\ 70:x=1\\ x=70:1\\ x=70\\ d,\left[3\times\left(x+2\right):7\right]\times4=120\\ 3\times\left(x+2\right):7-120:4\\ 3\times\left(x+2\right):7=30\\ \left(x+2\right):7=30:3\\ \left(x+2\right):7=10\\ x+2=10\times7\\ x+2=70\\ x=70-2\\ x=68\)

a) 8 + 2x = 20

2x = 20 - 8

2x = 12

x = 12 : 2

x = 6

Vậy x = 6

b) 70 - 5(x - 3) = 45

5(x-3) = 70 - 45

5(x-3) = 25

x - 3 = 25 : 5

x - 3 = 5

x = 5 + 3

x = 8

Vậy x = 8

c) (3x - 2^4). 7^3 = 2. 7^4

(3x - 16) . 147 = 2 . 1029

(3x - 16) . 147 = 2058

3x - 16 = 2058 : 147

3x - 16 = 14

3x = 14 + 16

3x = 30

x = 30 : 3 

x = 10 

Vậy x = 10

a/ 8+2.x=20

    2x=20-8

    2x=12

   x=12:2=4

b/70-5.(x-3)=45

       5.(x-3)=70-45=25

          x-3=25:5=5

          x=5+3=8

c/(3.x-2⁴).7³=2.7⁴

  (3.x-2⁴).7³=4802

  3x-2⁴ =4802:7³=14

  3x=14+2⁴=30

  x=30:3=10

tk nhen

câu 1 là 6 nhé, mk nahaafm