Tìm số tự nhiên x, biết: \({\left( {x - 5} \right)^2} = \dfrac{{49}}{4}\)

* Hướng dẫn giải

Ta có:

\(\begin{array}{l}{\left( {x - 5} \right)^2} = \dfrac{{49}}{4}\\\,\,\,\,\,\,{\left( {x - 5} \right)^2} = {\left( {\dfrac{7}{2}} \right)^2}\end{array}\)

\(\Rightarrow \left[ \begin{array}{l}x - 5 = \dfrac{7}{2}\\x - 5 = \dfrac{{ - 7}}{2}\end{array} \right.\)\( \Rightarrow \left[ \begin{array}{l}x = \dfrac{7}{2} + 5\\x = \dfrac{{ - 7}}{2} + 5\end{array} \right.\)\( \Rightarrow \left[ \begin{array}{l}x = \dfrac{{17}}{2}\\x = \dfrac{3}{2}\end{array} \right.\)

Vậy \(x = \dfrac{{17}}{2} \,\, hoặc \,\,x = \dfrac{3}{2}.\)

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