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

x^3=125

x=5

x⁶:x³=125

x^6-3=125

x³=125

x³=5³

x=5

vậy x=5

thu gọn 7^3*7^5

Oh no nhiều kí tự đặc biệt quá

dễ quá mình ko làm  đc 

a 6/2x+1=2/7

    6/2 x+1= 2/7-1

      6/2 x=-5/7

       x   = -5/21

bài gì mà dài vậy

\(=>2\cdot4^x+64\cdot4^x=1056\)

\(=>4^x\cdot\left(2+64\right)=1056\)

\(=>4^x=1056:66=16\)

\(=>4^x=4^2\)

\(=>x=2\)

ti ck nha

2.2^2x + 4³.4^x = 1056

=> 2.4^x + 4³.4^x = 1056

=> (2 + 64).4^x = 1056

=> 66.4^x = 1056

=> 4^x = 1056 : 66

=> 4^x = 16

=> 4^x = 4²

=> x = 2

7.4^{x - 1} + 4^{x + 1} = 23

=> 7.4^x.1/4 + 4^x.4 = 23

=> (7/4 + 4).4^x = 23

=> 23/4.4^x = 23

=> 4^x = 23 : 23/4

=> 4^x = 4

=> x = 1

3^{x + 2} - 5.3^x = 36

=> 3^x.9 - 5.3^x = 36

=> 3^x.(9 - 5) = 36

=> 3^x.4 = 36

=> 3^x = 36 : 4

=> 3^x = 9 = 3²

=> 3^x = 2

\(7\cdot4^{x-1}+4^{x+1}=23\)

\(=>7\cdot4^x:4+4^x\cdot4=23\)

\(=>\frac{7}{4}\cdot4^x+4^x\cdot4=23\)

\(=>4^x\cdot\left(\frac{7}{4}+4\right)=23\)

\(=>4^x=23:\frac{23}{4}=4\)

\(=>4^x=4^1\)

\(=>x=1\)