Question

{x-y=3
{x+y=9
Пари чисел (7:4) (6:3)

Answer 1

метод подстановки:

$\displaystyle \left \{ {{x-y=3} \atop {x+y=9}} \right.\\ \\\left \{ {{x-y=3} \atop {x=9-y}} \right. \\\\9-y-y=3\\y=3\\x=9-3\\x=6\\(x,y)=(6,3)$