Question

Функция х+у=400
0,12х+0,28у=64

Answer 1

$left { {{x+y=400} atop {0,12x+0,28y=64}} right. ; left { {{x+y=400} atop {12x+28y=6400}} right. ; left { {{x+y=400} atop {3x+7y=1600}} right. ; left { {{-3x-3y=-1200} atop {3x+7y=1600}} right. ; ; +\\ left { {{x+y=400} atop {4y=400}} right. ; left { {{x+y=400} atop {y=100}} right. ; left { {{x=300} atop {y=100}} right.$