Odpowiedź :
[tex]A(2,1)\\B(-1, -3)\\\left \{ {{1=2a+b} \atop {-3=-1a+b /*(-1)}} \right. \\+\left \{ {{1=2a+b} \atop {3=1a-b}} \right. \\1+3=2a+1a\\4=3a /:3\\\frac43=a\\1=2*\frac43+b\\1=\frac83+b /-\frac83\\\frac33-\frac83=b\\-\frac53=b\\y=\frac43x-\frac53[/tex]