Question

Số cặp số nguyên (x,y) thỏa mãn 2x^2y-4x^2+y-5=0 là ?

Answer 1

\(\Leftrightarrow2x^2y+y=4x^2+5\)

\(\Leftrightarrow y\left(2x^2+1\right)=4x^2+5\)

\(\Leftrightarrow y=\dfrac{4x^2+5}{2x^2+1}=2+\dfrac{3}{2x^2+1}\)

y nguyên \(\Rightarrow\dfrac{3}{2x^2+1}\) nguyên \(\Rightarrow2x^2+1=Ư\left(3\right)\)

Mà \(2x^2+1\ge1\Rightarrow\left[{}\begin{matrix}2x^2+1=1\\2x^2+1=3\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=0\Rightarrow y=5\\x=1\Rightarrow y=3\\x=-1\Rightarrow y=3\end{matrix}\right.\)