Question

\left \{ {{x^2+y^2=28} \atop {x+y=4}} \right.

Answer 1

$\left \{ {{x^2+y^2=28} \atop {y=4-x}} \right. \\ \left \{ {{y=4-x} \atop {x^2-4x-6=0}} \right. \\ \left \{ {{x= 2+ \sqrt{10} } } \atop {y=2-\sqrt{10}}} \right. ---or--- \left \{ {{x=2-\sqrt{10}} \atop {y=2+\sqrt{10}}} \right.$