x+20%*x=7,2

=> x.100%-20%.x=7,2

=>x.(100%-20%)=7,2

=>x.80%  =7,2

=> x=7,2:80%

=> x=9

x + 20%.x = 72 

<=> 120% .x = 7,2

x = 7,2 : 120 . 100 = 6

Ta có : x + 20% * x = 7,2

            x + 1/5 * x  = 7,2

            x( 1/5 +1)   = 7,2

            x * 6/5        = 7,2

                     x        =  6

x-20%*x=7.2 

=>  x .100 % - 20%.x = 7.2

=> x .(100% -20% ) = 7.2

=> x . 80% = 7.2

=> x = 7.2 : 80 % 

=> x = 9

\(x-20\%\times x=7,2\)

\(x-\frac{1}{5}\times x=7,2\)

\(x\times\left(1-\frac{1}{5}\right)=7,2\)

\(x\times\frac{4}{5}=7,2\)

\(x=7,2:\frac{4}{5}\)

\(x=9\)

x-20%*x=7.2 

=>  x .100 % - 20%.x = 7.2

=> x .(100% -20% ) = 7.2

=> x . 80% = 7.2

=> x = 7.2 : 80 % 

=> x = 9

X + 0,2 x X = 7,2

1,2 x X = 7,2

X = 7,2 : 1,2

X = 6

Đúng 100%

Đúng 100%

Đúng 100%

Ta có: \(x+20\%x=7,2\)

<=>\(x+0,2x=7,2\)

<=>\(x\left(1+0,2\right)=7,2\)

<=>\(1,2x=7,2\)

<=>\(x=7,2:1,2\)

<=>\(x=6\)

Vậy:\(x=6\)

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

6,5454545454..còn phân sô là :72/11 tích mình nha

\(x\div6\times7,2+1,3\times x+x\div2+15=19,95\)

\(\Leftrightarrow x\times\frac{1}{6}\times7,2+1,3\times x+x\times\frac{1}{2}=19,95-15\)

\(\Leftrightarrow x\times1,2+x\times1,3+x\times\frac{1}{2}=4,95\)

\(\Leftrightarrow x\times\left(1,2+1,3+\frac{1}{2}\right)=4,95\)

\(\Leftrightarrow x\times3=4,95\)

\(\Leftrightarrow x=4,95\div3\)

\(\Leftrightarrow x=1,65\)

Vậy x = 1,65

y x (7,2 - 6,2 )

y x 1

y = 1

y=1

 h minh nhe minh se h lai

y=1

tk các bạn