Question

Tìm số tự nhiên x, biết:

(2x + 1)(y - 3) = 15

Answer 1

\(\Rightarrow\left(2x+1\right)\left(y-3\right)=15=1\cdot15=3\cdot5\)

Với \(x\in N\Rightarrow2x+1\ge1;2x+1\) lẻ

\(\left\{{}\begin{matrix}2x+1=1\\y-3=15\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\\y=18\end{matrix}\right.\\ \left\{{}\begin{matrix}2x+1=15\\y-3=1\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=7\\y=4\end{matrix}\right.\\ \left\{{}\begin{matrix}2x+1=3\\y-3=5\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=1\\y=8\end{matrix}\right.\\ \left\{{}\begin{matrix}2x+1=5\\y-3=3\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=3\\y=6\end{matrix}\right.\)

Vậy \(x\in\left\{0;1;3;7\right\}\)