Решите систему уравнений

Решите задачу:

$x-y=7;\\\\y=x-7;\\\\x^2+y^2=9-2xy;\\\\x^2+(x-7)^2=9-2x(x-7);\\\\x^2+x^2-14x+49=9-2x^2+14x;\\\\4x^2-28x+40=0;\\\\x^2-7x+8=0;\\\\D=(-7)^2-4*1*8=49-32=17;\\\\x_1=\frac{7+\sqrt{17}}{2};\\\\x_2=\frac{7-\sqrt{17}}{2};\\\\y_1=\frac{7+\sqrt{17}}{2}-7=\frac{-7+\sqrt{17}}{2};\\\\y_2=\frac{7-\sqrt{17}}{2}-7=\frac{-7-\sqrt{17}}{2};\\\\(\frac{7+\sqrt{17}}{2};\frac{-7+\sqrt{17}}{2}); (\frac{7-\sqrt{17}}{2};\frac{-7-\sqrt{17}}{2})$