Question

Способ сложения

x+y=7
x-y=13

Answer 1

$\left \{ {{x+y=7} \atop {x-y=13}} \right. \\\\ \left \{ {{x+y+x-y=7+13} \atop {x+y=7}} \right. \\\\ \left \{ {{2x=20} \atop {y=7-x}} \right. \\\\ \left \{ {{x=10} \atop {y=7-10=-3}} \right. \\\\ \left \{ {{x=10} \atop {y=-3}} \right.$

Ответ: $(10;\ -3)$