Question

tìm x, biết:

a/ x/-27 = -3/x

b/ -9/x = -x/ 4/49

Answer 1

a. \(\dfrac{x}{-27}=\dfrac{-3}{x}\)

\(\Leftrightarrow xx=\left(-27\right)\left(-3\right)\)

\(\Leftrightarrow x^2=81\)

\(\Leftrightarrow\left[{}\begin{matrix}x^2=9^2\\x^2=\left(-9\right)^2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=9\\x=-9\end{matrix}\right.\)

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Answer 2

\(\dfrac{x}{-27}=\dfrac{-3}{x}\)

\(\Rightarrow x^2=81\)

\(\Rightarrow\left[{}\begin{matrix}x=9\\x=-9\end{matrix}\right.\)

\(\dfrac{-9}{x}=\dfrac{-x}{\dfrac{4}{49}}\)

\(\Rightarrow-x^2=\dfrac{-36}{49}\)

\(-x^2\ge0;\dfrac{-36}{49}< 0\)

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