Question

1. Resolva o sistema:
x+y=3
x-y=1

2. Resolva o sistema:
x+y=20
3x+4y=72
3. Resolva o sistema:
2x+3y=5
x-4y=8
4. Resolva o sistema:
2x+3y=19
x-y=-3
5. Resolva o sistema:
x+y=10
x-y=12

Answer 1

1)x + y = 3
x = 3 - y
x - y = 1
3 - y - y = 1
-2y = -2 (-1)
y = 1
x = 2

2)x + y = 20
x = 20 - y
3x + 4y = 72
3(20 - y) + 4y = 72
60 - 3y + 4y = 72
y = 12
x = 8

3)x - 4y = 8
x = 8 + 4y
2x + 3y = 5
2(8 + 4y) + 3y = 5
16 + 8y + 3y = 5
11y = 11
y = 1
x = 12

4)x - y = -3
x = -3 + y
2x + 3y = 19
2(-3 + y) + 3y = 19
-6 + 2y + 3y = 19
5y = 25
y = 5
x = 2

5)x + y = 10
x = 10 - y
10 - y - y = 12
-2y = 2 (-1)
2y = -2
y = -1
x = 11