Question

решите систему уравнений: x+y=4,x^2-y^2=8

Answer 1

$left { {{x+y=4} atop {x^2-y^2=8}} right.$
$x^{2}-y ^{2}=(x-y)(x+y)=4(x-y)=8$
x-y=2;
$left { {{x=2+y} atop {2+2y=4}} right.$
$left { {{y=1} atop {x=3}} right.$