Question

1)x + y = 25
x - y = 13

2)x + y = 20
x - y = 8

Answer 1

1)
{x+y=25
{x-y=13
---------------
2x-0=38
2x=38
x=38/2
x=19

x+y=25
19+y=25
y=25-19
y=6

S={6;19}

2)
{x+y=20
{x-y=8
-------------
2x-0=28
2x=28
x=28/2
x=14

x+y=20
14+y=20
y=20-14
y=6

S={6;14}

Nota: Usei o método de adição.

Answer 2

1) x + y = 25 (I)
x - y = 13 (II)
__________
2x = 38
x = 38/2 .: x = 19
Substituindo em (I)
19 + y = 25
y = 25 - 19 .: y = 6

V = (6; 19)

2) x+y=20 (I)
x-y=8 (II)
_________
2x= 28
x = 14
Subs. Em (I)
14+y= 20
y = 6

V = (6;14)