Question

решите систему x+y=7
5x-7y=14

Answer 1

{x+y=7 {5x-7y=14
y=7-x
5x-7 (7-x)=14
5x-49+7x=14
12x-49=14
12x=14+49
12x=63
x=63/12=21/4

y=7-21/4=(28-21)/4=7/4

Ответ:x=21/4 y=7/4