X^2+y^2+2xy=9, x-y=1 решить систему методом сложения

Решите задачу:

$\left \{ {{x^2+y^2+2xy=9} \atop {x-y=1}} \right. \; \left \{ {{(x+y)^2=9} \atop {x-y=1}} \right. \; \left \{ {{x+y=\pm 3} \atop {x-y=1}} \right. \\\\a)\; \; \left \{ {{x+y=3} \atop {x-y=1}} \right. \; \oplus \; \left \{ {{x+y=3} \atop {2x=4}} \right. \; \left \{ {{y=3-x} \atop {x=2}} \right. \; \left \{ {{y=1} \atop {x=2}} \right.$

$b)\; \; \left \{ {{x+y=-3} \atop {x-y=1}} \right. \; \oplus \left \{ {{x+y=-3} \atop {2x=-2}} \right. \left \{ {{y=-3-x} \atop {x=-1}} \right. \; \left \{ {{y=-2} \atop {x=-1}} \right.$

$Otvet:\; \; (2,1)\; ,\; \; (-1,-2)\; .$