Question

решите систему методом подстановки х-у=7, x+y=11

Answer 1

$\left \{ {{x - y = 7} \atop {x + y = 11}} \right.$

$\left \{ {{x = 7 + y} \atop {(7 + y) + y = 11}} \right.$

$(7 + y) + y = 11\\7 + y + y = 11\\7 + 2y = 11\\2y = 11 - 7\\2y = 4\\y = 2$

$\left \{ {{x = 7 + y} \atop {y = 2}} \right.$

$\left \{ {{x = 7 + 2} \atop {y = 2}} \right.$

$\left \{ {{x = 9} \atop {y = 2}} \right.$