Как решить? {X+Y=10 {x2-y2=40

$\left \{ {{x+y=10} \atop {x^2-y^2=40}} \right. \\\left \{ {{x+y=10} \atop {(x-y)(x+y)=40}} \right. \\ \left \{ {{x+y=10} \atop {(x-y)*10=40}} \right. \\ \left \{ {{x+y=10} \atop {x-y=4}} \right. \\ \left \{ {{x=10-y} \atop {10-y-y=4}} \right. \\ \left \{ {{x=10-y} \atop {10-2y=4}} \right. \\ \left \{ {{x=10-y} \atop {2y=6}} \right. \\ \left \{ {{x=10-y} \atop {y=3}} \right. \\ \left \{ {{x=7} \atop {y=3}} \right.$
проверяем:
$\left \{ {{7+3=10} \atop {7^2-3^2=49-9=40}} \right.$
ответ: (7;3)