Question

решите систему линейных уравнений методом подстановки x+y=7 5x-7y=11

Answer 1

x+y=7
5x-7y=11

x=7-y
5(7-y) - 7y=11 

35-5y-7y=11

-12y=-24

y=2 
x= 7-2=5 

Answer 2

$left { {{x+y=7} atop {5x-7y=11}} right.; left { {{x=7-y} atop {5(7-y)-7y=11}} right.$

5(7-y)-7y-11=0

35-5y-7y-11=0

-12y+24=0

y=-2

x=7-y=7-2=5