Question

помогите решить систему {2x+y=5 {x-y=7

Answer 1

$left { {{2x+y=5} atop {x-y=7}} right. ; left { {{3x=12} atop {x-y=7}} right. ; ; left { {{x=4} atop {4-y=7}} right. ; ; left { {{x=4} atop {y=-3}} right.$

Answer 2

$left { {{2x+y=5} atop {x-y=7}} right. \ \ left { {{2(7+y)+y=5} atop {x=7+y}} right. \ \ left { {{14+2y+y=5} atop {x=7+y}} right. \ \ left { {{y=-3} atop {x=7+(-3)}} right. \ \ left { {{y=-3} atop {x=4}} right.$