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

a)\(8+2x=20\)

   \(2x=14\)

     \(x=\frac{14}{2}=7\)

               vậy x=7

b)\(70-5\left(x+3\right)=45\)

    \(5\left(x+3\right)=25\)

     \(x+3=5\)

    \(x=2\)

             Vậy \(x=2\)

c)\(\left(3x-2^4\right).7^3=2.7^4\)

    \(\left(3x-16\right)=\frac{2.7^4}{7^3}\)

    \(3x-16=7.2\)

     \(3x-16=14\)

      \(3x=30\)

       \(x=10\)

              Vậy \(x=10\)

2: Tìm x

a) Ta có: x+25=40

nên x=40-25=15

Vậy: x=15

b) Ta có: 198-(x+4)=120

\(\Leftrightarrow x+4=198-120=78\)

hay x=78-4=74

Vậy: x=74

c) Ta có: \(\left(2x-7\right)\cdot3=125\)

\(\Leftrightarrow2x-7=\dfrac{125}{3}\)

\(\Leftrightarrow2x=\dfrac{125}{3}+7=\dfrac{125}{3}+\dfrac{21}{3}=\dfrac{146}{3}\)

\(\Leftrightarrow x=\dfrac{146}{3}:2=\dfrac{146}{6}=\dfrac{73}{3}\)

Vậy: \(x=\dfrac{73}{3}\)

d) Ta có: \(x+16⋮x+1\)

\(\Leftrightarrow x+1+15⋮x+1\)

mà \(x+1⋮x+1\)

nên \(15⋮x+1\)

\(\Leftrightarrow x+1\inƯ\left(15\right)\)

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

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

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

\(a,x+25=40\\ \Rightarrow x=40-25\\ \Rightarrow x=15\\ b,198-\left(x+4\right)=120\\ \Rightarrow-\left(x+4\right)=120-198\\ \Rightarrow-\left(x+4\right)=-78\\ \Rightarrow x+4=78\\ \Rightarrow x=78-4\\ \Rightarrow x=74\\ c,\left(2x-7\right).3=125\\ \Rightarrow2x-7=\dfrac{125}{3}\\ \Rightarrow2x=\dfrac{125}{3}+7\\ \Rightarrow2x=\dfrac{146}{3}\\ \Rightarrow x=\dfrac{146}{3}:2\Rightarrow x=\dfrac{73}{3}\\ d,\left(x+16\right)⋮\left(x+1\right)\\ \Rightarrow\left[\left(x+1\right)+15\right]⋮\left(x+1\right)\\ mà:\left(x+1\right)⋮\left(x+1\right)\\ \Rightarrow15⋮\left(x+1\right)\\ \Rightarrow\left(x+1\right)\inƯ\left(15\right)\\ \Rightarrow\left(x+1\right)\in\left\{-15;-1;1;15\right\}\\ \Rightarrow x\in\left\{-16;-2;0;14\right\}\)

Tự kết luận nhé bạn

1: =>3^x=81

=>x=4

2: =>2^x=8

=>x=3

3: =>x^3=2^3

=>x=2

4: =>x^20-x=0

=>x(x^19-1)=0

=>x=0 hoặc x=1

5: =>2^x=32

=>x=5

6: =>(2x+1)^3=9^3

=>2x+1=9

=>2x=8

=>x=4

7: =>x^3=115

=>\(x=\sqrt[3]{115}\)

8: =>(2x-15)^5-(2x-15)^3=0

=>(2x-15)^3*[(2x-15)^2-1]=0

=>2x-15=0 hoặc (2x-15)^2-1=0

=>2x-15=0 hoặc 2x-15=1 hoặc 2x-15=-1

=>x=15/2 hoặc x=8 hoặc x=7

1. Tìm số tự nhiên x biết:

1) \(3^x.3=243\)

\(3^x=243:3\)

\(3^x=81\)

\(3^x=3^4\)

\(\Rightarrow x=4\)

_____

2) \(7.2^x=56\)

\(2^x=56:7\)

\(2^x=8\)

\(2^x=2^3\)

\(\Rightarrow x=3\)

_____

3) \(x^3=8\)

\(x^3=2^3\)

\(\Rightarrow x=3\)

_____

4) \(x^{20}=x\)

\(x^{20}-x=0\)

\(x\left(x^{19}-1\right)=0\)

\(\Rightarrow x=0\) hoặc \(x=1\)

5) \(2^x-15=17\)

\(2^x=17+15\)

\(2^x=32\)

\(2^x=2^5\)

\(\Rightarrow x=5\)

_____

6) \(\left(2x+1\right)^3=9.81\)

\(\left(2x+1\right)^3=729=9^3\)

\(\rightarrow2x+1=9\)

\(2x=9-1\)

\(2x=8\)

\(x=8:2\)

\(\Rightarrow x=4\)

_____

7) \(x^6:x^3=125\)

\(x^3=125\)

\(x^3=5^3\)

\(\Rightarrow x=5\)

_____

8) \(\left(2x-15\right)^5=\left(2x-15\right)^3\)

\(\rightarrow\left(2x-15\right)^5-\left(2x-15\right)^3=0\)

\(\left(2x-15\right)^3.\left[\left(2x-15\right)^2-1\right]=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}\left(2x-15\right)^3=0\\\left(2x-15\right)^2-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{15}{2}\\x=7\\x=8\end{matrix}\right.\)

_____

9) \(3^{x+2}-5.3^x=36\)

\(3^x.\left(3^2-5\right)=36\)

\(3^x.\left(9-5\right)=36\)

\(3^x.4=36\)

\(3^x=36:4\)

\(3^x=9\)

\(3^x=3^2\)

\(\Rightarrow x=2\)

_____

10) \(7.4^{x-1}+4^{x+1}=23\)

\(\rightarrow7.4^{x-1}+4^{x-1}.4^2=23\)

\(4^{x-1}.\left(7+4^2\right)=23\)

\(4^{x-1}.\left(7+16\right)=23\)

\(4^{x-1}.23=23\)

\(4^{x-1}=23:23\)

\(4^{x-1}=1\)

\(4^{x-1}=4^1\)

\(\rightarrow x-1=0\)

\(x=0+1\)

\(\Rightarrow x=1\)

Chúc bạn học tốt

a) 2x + 15 = 45

2x = 45 - 15

2x = 30

x = 30 : 2

x = 15 (nhận)

Vậy x = 15

b) 120 - 2.(x + 3) = 22.52

120 - 2.(x + 3) = 1144

2.(x + 3) = 120 - 1144

2.(x + 3) = - 1024

x + 3 = -1024 : 2

x + 3 = -512

x = - 512 - 3

x = -515 (loại)

Vậy không tìm được x thỏa mãn x là số tự nhiên

c) 11 ⋮ (x - 2)

⇒ x - 2 ∈ Ư(11) = {-11; -1; 1; 11}

⇒ x ∈ {-9; 1; 3; 13}

Do x là số tự nhiên

⇒ x ∈ {1; 3; 13}

d) Do 12 ⋮ x và 18 ⋮ x nên x ∈ ƯC(12; 18)

12 = 2².3

18 = 2.3²

ƯCLN(12; 18) = 2.3 = 6

⇒ x ∈ ƯC(12; 18) = {1; ; 3; 6}

1: =>5(2x+6)=40

=>2x+6=8

=>2x=2

=>x=1

2: =>12-(x+3)=256:64=4

=>(x+3)=8

=>x=5

3: =>2x-1=3 hoặc 2x-1=-3

=>x=2 hoặc x=-1

4: \(\Leftrightarrow3^{x+2017}=3^{2015}\)

=>x+2017=2015

=>x=-2

1: =>5(2x+6)=40

=>2x+6=8

=>2x=2

=>x=1

2: =>12-(x+3)=256:64=4

=>(x+3)=8

=>x=5

3: =>2x-1=3 hoặc 2x-1=-3

=>x=2 hoặc x=-1

4: \Leftrightarrow3^{x+2017}=3^{2015}⇔3x+2017=32015

=>x+2017=2015

=>x=-2

a) (3x-15)⁷ = 0

3x-15 = 0

3x = 0+15

3x = 15

x = 15:3

x = 5

b) 4^2x-6 = 1

<=> 2x-6 = 0

2x = 0+6

2x = 6

x = 6:2

x = 3

a) (3x-15)⁷ = 0

3x-15 = 0

3x = 0+15

3x = 15

x = 15:3

x = 5

b) 4^{2x - 6} = 1

<=> 2x-6 = 0

2x = 0+6

2x = 6

x = 6:2

x = 3

\(\left(x+2\right)-2=0\)

\(\Rightarrow x+2-2=0\)

\(\Rightarrow x=0\)

\(\left(x+3\right)+1=7\)

\(\Rightarrow x+3+1=7\)

\(\Rightarrow x+4=7\)

\(\Rightarrow x=3\)

\(\left(3x-4\right)+4=12\)
\(\Rightarrow3x-4+4=12\)

\(\Rightarrow3x=12\)

\(\Rightarrow x=4\)

\(\left(5x+4\right)-1=13\)

\(\Rightarrow5x+4-1=13\)

\(\Rightarrow5x+3=13\)

\(\Rightarrow5x=10\)

\(\Rightarrow x=2\)

\(\left(4x-8\right)-3=5\)

\(\Rightarrow4x-8-3=5\)

\(\Rightarrow4x-11=5\)

\(\Rightarrow4x=16\)

\(\Rightarrow x=4\)

\(8-\left(2x+4\right)=2\)

\(\Rightarrow8-2x-4=2\)

\(\Rightarrow4-2x=2\)

\(\Rightarrow2x=2\)

\(\Rightarrow x=1\)

\(7+\left(5x+2\right)=14\)

\(\Rightarrow7+5x+2=14\)

\(\Rightarrow9+5x=14\)

\(\Rightarrow5x=5\)

\(\Rightarrow x=1\)

\(5-\left(3x-11\right)=1\)

\(\Rightarrow5-3x+11=1\)

\(\Rightarrow16-3x=1\)

\(\Rightarrow3x=15\)

\(\Rightarrow x=5\)

2\(^x\)- 15 = 17

\(\Rightarrow\)2\(^x\) =  32

\(\Rightarrow\)x  = 5

2^x-15=17

=>2^x=17+15

=2^x=32

=>2^x=2^5

=>x=5