Question

х+у=10

х в кв -у в кв=40

Answer 1

$left { {{y=10-x} atop {x^2-(10-x)^2=40}} right. left { {{y=10-x} atop {x^2-100+20x-x^2=40}} right.\\ left { {{y=10-x} atop {20x=140}} right. left { {{y=10-x} atop {x=7 }} right. left { {{y=3} atop {x=7}} right.$