Question

Tìm x:

\(\dfrac{x-1}{15}=\dfrac{60}{x-1}\)

Answer 1

\(\dfrac{x-1}{15}=\dfrac{60}{x-1}\)
\(\Rightarrow\left(x-1\right)^2=60.15\)
\(\Rightarrow\left(x-1\right)^2=900\)
\(\Rightarrow\left(x-1\right)^2=30^2\) 
\(\Rightarrow x-1=30\) hoặc \(x-1=-30\)
\(\Rightarrow x=31\) hoặc \(x=-29\)
Vậy ...

Answer 2

\(\dfrac{x-1}{15}=\dfrac{60}{x-1}\) (ĐK: \(x\ne1\))

\(\Leftrightarrow\left(x-1\right)\left(x-1\right)=15\cdot60\)

\(\Leftrightarrow\left(x-1\right)^2=900\)

\(\Leftrightarrow\left(x-1\right)^2=30^2\)

\(\Leftrightarrow\left|x-1\right|=30\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=30\\x-1=-30\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=31\\x=-29\end{matrix}\right.\)(T/m)