Помогите ршить систему уравнений пожалуйста

$\left \{ {{x+y=10} \atop {xy=21}} \right. \left \{ {{x=10-y} \atop {(10-y)y=21}} \right. \left \{ {{x=10-y} \atop {10y- y^{2} =21}} \right. \\ y^{2}-10y+21=0 \\ \left \{ {{y_{1}+y_{2}=10} \atop {y_{1}*y_{2}=21 }} \right. \left \{ {{y_{1}=3} \atop {y_{2}=7 }} \right. \\ x_{1}=7; \\ x_{2}=3.$
Ответ: (7;3), (3;7).