Question

Resolva o sistema de equaçao

X+y=11
X-y=3

X-y=5
X+y=7

Answer 1

x+y=11
x-y= 3 >> somando as duas tem:
2x= 14
x=14/2
x= 7  >> Substituindo 
x-y=3 -> 7-y=3 -> -y= -7+3 ->  -y= -4 (-1)    y=4

--------------------------------
x-y=5
x+y=7
2x= 12
x=12/2
x=6  
 
x+y=7
6+y=7
y= 7-6
y=1

Answer 2

x+y=11.
x=11-y
x=11-4
x=7

x-y=3
11-y-y=3
-2y=3-11
-2y=8
y=4

x-y=5
x=5+y
x=5+1
x=6

x+y=7
5+y+y=7
2y=7-5
2y=2
y=1