Способом подстановки решите систему уравнений {x^2+y^2=7 3x^2-y^2=9

$\left \{ {{ x^{2} + 7^{2} =7} \atop {3 x^{2} - y^{2}=9 }} \right. +, \left \{ {{ x^{2} + y^{2}=7 } \atop {4 x^{2} =16}} \right. , \left \{ {{ x^{2} + y^{2}=7 } \atop { x^{2} =4}} \right. , \left \{ {{ x^{2} + y^{2} =7} \atop {x=-+2}} \right.$
$1. \left \{ {{ x_{1} =-2} \atop { y^{2} =3}} \right. \left \{ {{ x_{1} =-2} \atop {y=-+ \sqrt{3} }} \right. 2. \left \{ {{ x_{2}=2 } \atop { y^{2}=3 }} \right. \left \{ {{ x_{2} =2} \atop {y=-+ \sqrt{3} }} \right.$
ответ: (-2;-√3), (-2;√3), (2;-√3), (2;√3)

$\left \{ {{ x^{2} + y^{2}=7 } \atop { 3x^{2} - y^{2}=9 }} \right. , \left \{ {{ x^{2} =7- y^{2} } \atop {3*(7- y^{2} )- y^{2} =9}} \right.$
-4y²=-12, y²=3. y=-+√3
x²=4. x=-+2

ответ: (-2;-√3), (-2;√3), (2;-√3), (2;√3)