[tex]\it 1.\ \begin{cases}\it x+y=1\\ \\ \it xy=-2\end{cases}\\ \\ s=x+y=1\\ \\ p=xy=-2[/tex]
Vom rezolva ecuația:
[tex]\it t^2-st+p=0 \Rightarrow t^2+t-2=0 \Rightarrow t^2+t-2t-2=0 \Rightarrow \\ \\ \Rightarrow t(t+1)-2(t+1)=0 \Rightarrow (t+1)(t-2)=0 \Rightarrow t_1=-1,\ \ t_2=2\\ \\ (x,y)\in\{(-1,\ 2),\ (2,\ -1)\}[/tex]
