Question

tìm x:

a)\(\left|x-3,5\right|=7,5\)

b)\(9^x:3^x=81\)

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

d)\(\frac{-2}{x}=\frac{-x}{\frac{8}{25}}\)

Answer 1

a) |x-3,5| = 7,5

\(\Rightarrow\hept{\begin{cases}x-3,5=7,5\\x-3,5=-7,5\end{cases}}\Rightarrow\hept{\begin{cases}x=11\\x=-4\end{cases}}\)

b) 9^x:3^x = 81

=> (3²)^x:3^x = 3⁴

3^2x : 3^x = 3⁴

<=> 3^2x-x = 3⁴

2x-x = 4

<=> x = 4

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

\(x=\left(\frac{-1}{3}\right).\left(\frac{-1}{3}\right)^3\)

\(x=\left(\frac{-1}{3}\right)^4=\frac{\left(-1\right)^4}{3^4}=\frac{1}{81}\)

d) \(\frac{-2}{x}=\frac{-x}{\frac{8}{25}}\)

=> -2x = (-2).\(\frac{8}{25}\)

-2x = \(\frac{-16}{25}\)

=> 2x = \(-\left(\frac{-16}{25}\right)\)

\(x=\frac{16}{25}:2\)

x= \(\frac{8}{25}\)