Question

tìm x , y

(xy-1)(y+1)=3

Answer 1

Ta có: (xy-1)(y+1)=3=1.3=3.1=(-1).(-3)=(-3).(-1)

\(\Rightarrow\left[{}\begin{matrix}xy-1=1;y+1=3\\xy-1=3;y+1=1\\xy-1=\left(-1\right);y+1=\left(-3\right)\\xy-1=\left(-3\right);y+1=\left(-1\right)\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}xy=2;y=2\Leftrightarrow x=1;y=2\\xy=4;y=0\Leftrightarrow x=4:0;y=0\left(lạoi\right)\\xy=0;y=\left(-4\right)\Leftrightarrow x=0;y=\left(-4\right)\\xy=\left(-2\right);y=\left(-2\right)\Leftrightarrow x=1;y=\left(-2\right)\end{matrix}\right.\)

Vậy: \(\left[{}\begin{matrix}x=1;y=2\\x=0;y=\left(-4\right)\\x=1;y=\left(-2\right)\end{matrix}\right.\)