Question

решите систему уравнений x+y=7 x^2-y^2=21

Answer 1

$left { {{x+y=7} atop {x^2-y^2=21}} right.$
$left { {{x+y=7} atop {(x-y)(x+y)=21}} right.$
$left { {{x+y=7} atop {(x-y)*7=21}} right.$
$left { {{x+y=7} atop {x-y=3}} right.$
$left { {{2x=10} atop {y=x-3}} right.$
$left { {{x=5} atop {y=5-3}} right.$
$left { {{x=5} atop {y=2}} right.$

Ответ: (5;2)