Question

Tìm x, y thuoc Z biet

xy + 3x - 7y = 21

Answer 1

Ta có : \(xy+3x-7y=21\)

\(\Leftrightarrow xy+3x-7y-21=0\)

\(\Leftrightarrow x\left(y+3\right)-7\left(y+3\right)=0\)

\(\Leftrightarrow\left(x-7\right)\left(y+3\right)=0\)

\(\Rightarrow x-7=0\)

\(\Leftrightarrow x=0+7\)

\(\Leftrightarrow x=7\)

\(\Rightarrow y+3=0\)

\(\Leftrightarrow y=0-3\)

\(\Leftrightarrow y=-3\)

\(\text{Vậy }\orbr{\begin{cases}x=7;y\inℤ\\x\inℤ;y=-3\end{cases}}\)