Question

Tìm số nguyên x biết \(\dfrac{4}{x}=\dfrac{x}{4}\)

 

Answer 1

\(\Leftrightarrow x^2=16\)

hay \(x\in\left\{4;-4\right\}\)

Answer 2

\(\dfrac{4}{x}=\dfrac{x}{4}\)

\(4x.\dfrac{4}{x}=4x.\dfrac{x}{4}\)

\(4.4=x.x\)

\(16=x.x\)

\(16=x^2\)

\(16-x^2=0\)

\(\Rightarrow x\in\left\{4;\left(-4\right)\right\}\)