Question

tìm x thuộc Q

a 0.4:x=x:0.9

Answer 1

Giải:

\(0,4:x=x:0,9\)

\(\Leftrightarrow\dfrac{0,4}{x}=\dfrac{x}{0,9}\)

\(\Leftrightarrow x.x=0,4.0,9\)

\(\Leftrightarrow x^2=0,36\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0,6\\x=-0,6\end{matrix}\right.\)

Vậy ...

Answer 2

\(\dfrac{2}{\dfrac{5}{x}}=\dfrac{x}{\dfrac{9}{10}}\)\(\Rightarrow\)x^2=\(\dfrac{2}{5}.\dfrac{9}{10}=\dfrac{9}{25}\)

Nên x=\(\dfrac{3}{5}\)hoặc x=\(\dfrac{-3}{5}\)