\(\frac{x^7}{81}=27\)

=> x⁷  = 27.81

    x⁷    = 3³.3⁴

=>   x⁷  = 3⁷

=> x = 3

Vũ Hồng Linh bạn check lại bài đầu dùm =_=" 

\(\left[-\frac{1}{3}\right]^3\cdot x=\frac{1}{81}\)

\(\Leftrightarrow x=\frac{1}{81}:\left[-\frac{1}{3}\right]^3\)

\(\Leftrightarrow x=\frac{1}{81}:\left[-\frac{1}{27}\right]\)

\(\Leftrightarrow x=\frac{1}{81}\cdot(-27)=-\frac{1}{3}\)

\(\left[x-\frac{1}{2}\right]^3=\frac{1}{27}\)

\(\Leftrightarrow\left[x-\frac{1}{2}\right]^3=\left[\frac{1}{3}\right]^3\)

=> Làm nốt 

Mấy bài kia cũng làm tương tự

(- \(\dfrac{1}{3}\))³.\(x\) = \(\dfrac{1}{81}\)

          \(x=\dfrac{1}{81}\) : (- \(\dfrac{1}{3}\))³

          \(x\) =  - (\(\dfrac{1}{3}\))⁴ :(\(\dfrac{1}{3}\))³

           \(x=-\dfrac{1}{3}\)

Vậy \(x=-\dfrac{1}{3}\)

(3\(x\) + 1)³ =  - 27

(3\(x\) + 1)³ = (-3)³

3\(x\) + 1 = -3

 3\(x\)       = - 3 - 1

 3\(x\) = -4

    \(x=-\dfrac{4}{3}\)

Vậy \(x=-\dfrac{4}{3}\)

\(\frac{x^7}{81}\) = 27

x⁷ : 81 = 27

x⁷        = 27 . 81 = 3³ . 3⁴

x⁷         = 3⁷

Suy ra : x = 3

Bài 2 :

   \(\frac{x^8}{9}\) = 729

x⁸ : 9     = 729

x⁸          =  729 . 9

x⁸          =     3⁶ . 3²

x⁸              =              3⁸

Suy ra : x = 3

=>\(5\cdot\dfrac{3\sqrt{x-3}}{5}-7\cdot\dfrac{2\sqrt{x-3}}{3}-7\cdot\sqrt{x^2-9}+18\cdot\sqrt{\dfrac{9}{81}\left(x^2-9\right)}=0\)

=>\(3\cdot\sqrt{x-3}-\dfrac{14}{3}\sqrt{x-3}=7\cdot\sqrt{x^2-9}-18\cdot\dfrac{3}{9}\cdot\sqrt{x^2-9}\)

=>\(-\dfrac{5}{3}\sqrt{x-3}=\sqrt{x^2-9}\)

=>\(\sqrt{x-3}\left(\sqrt{x+3}+\dfrac{5}{3}\right)=0\)

=>x-3=0

=>x=3

a)\(\left(\frac{3}{5}\right)^5\times x=\left(\frac{3}{7}\right)^7\)

\(\Leftrightarrow\frac{3^5}{5^5}\times x=\frac{3^7}{7^7}\)

\(\Leftrightarrow x=\frac{3^7}{7^7}:\frac{3^5}{5^5}\)

\(\Leftrightarrow x=\frac{3^7\times5^5}{7^7\times3^5}\)

\(\Leftrightarrow x=\frac{3^2\times5^5}{7^7}\)

b)\(\left(\frac{-1}{3}\right)^3\times x=\frac{1}{81}\)

\(\Leftrightarrow\frac{\left(-1\right)^3}{3^3}\times x=\frac{1}{3^4}\)

\(\Leftrightarrow x=\frac{1}{3^4}:\frac{-1}{3^3}\)

\(\Leftrightarrow x=\frac{1\times3^3}{3^4\times\left(-1\right)}\)

\(\Leftrightarrow x=\frac{1}{-3}\)

c)\(\Leftrightarrow\left(x-\frac{1}{2}\right)^3=\left(\frac{1}{3}\right)^3\)

\(\Leftrightarrow x-\frac{1}{2}=\frac{1}{3}\)

\(\Leftrightarrow x=\frac{1}{3}+\frac{1}{2}\)

\(\Leftrightarrow x=\frac{5}{6}\)

d)\(\Leftrightarrow\left(x+\frac{1}{2}\right)^4=\left(\frac{2}{3}\right)^4\)

\(\Leftrightarrow x+\frac{1}{2}=\frac{2}{3}\)

\(\Leftrightarrow x=\frac{2}{3}-\frac{1}{2}\)

\(\Leftrightarrow x=\frac{1}{6}\)

Ta có x⁷/81 = 27

=> x⁷ /3⁴ = 3³ 

=> x⁷ =3³.3⁴

=> x⁷=3⁷

=> x=3

\(\frac{x^7}{81}=27\)

=>x⁷ = 81 . 27

=>x⁷ = 2187

=>x⁷ = 3⁷

=>x = 3

Vậy x = 3

\(\frac{x^7}{81}=27\)

\(x^7=81\cdot27\)

\(x^7=2187\)

\(x^7=3^7\)

\(x=3\)

\(a,36.19+36.81\)

\(=36.\left(19+81\right)\)

\(=36.100\)

\(=3600\)

\(b,8.12.125.5\)

\(=\left(125.8\right)\left(12.5\right)\)

\(=1000.60\)

\(=60000\)

\(c,\)chịu 

c,7 x 9 + 14 x 27 + 21 x 36 / 21 x 27 + 42 x 81 + 63 x 108

7 x 9 + 14 x 27 + 21 x 36 / 7 x 3 x 9 x 3 + 14 x 3 x 27 x 3 + 21 x 3 x 36 x 3

1 / 3 x 3 + 3 x 3 + 3 x 3

1 / 9 + 9 + 9

1 / 27

mấy bọn nguuuuuuuuuuuuuuuuuuuuuuuu

a) \(\frac{x^7}{81}=27\)

=> x⁷ = 27.81

=> x⁷ = 3³.3⁴

=> x⁷ = 3⁷

=> x = 3

Vậy x = 3

b) \(\frac{x^8}{9}=729\)

=> x⁸ = 729.9

=> x⁸ = 3⁶.3²

=> x⁸ = 3⁸ = (-3)⁸

=> \(x\in\left\{3;-3\right\}\)

Vậy \(x\in\left\{3;-3\right\}\)