A) {X+y=10
{2x+3y=25
b) { x+y=16
{x+y=30
C) {2x-y=9
{x-y=4
D) {x+y=18
{x+2y=40
E) {3x+y=30
{x-y=19
Soluções para a tarefa
Resposta:
a)
2x + y = 10 (2)
3x - 2y = 1
4x + 2y = 20
3x - 2y = 1 (+)
------------------------
7x = 21
x = 21/7
x = 3
2x + y = 10
2.3 + y = 10
6 + y = 10
y = 10 - 6
y = 4
***************************
b)
2x + 3y = 10
4x - y = - 1 (3)
2x + 3y = 10
12x - 3y = - 3 (+)
----------------------------
14x = 7
x = 7 (:7)
------
14 (:7)
x = 1
-----
2
4x - y = - 1
4. 1 - y = - 1
----
2
4/2 - y = - 1
2 - y = - 1
2 + 1 = y
3 = y
y = 3
*****************************
c)
x + y = 20 (-2)
2x + 4y = 56
- 2x - 2y = - 40
2x + 4y = 56 (+)
-----------------------------
2y = 16
y = 16/2
y = 8
x + y = 20
x + 8 = 20
x = 20 - 8
x = 12
********************************
d)
x + y = 23 (-2)
2x + 4y = 82
- 2x - 2y = - 46
2x + 4y = 82
---------------------------
2y = 36
y = 36/2
y = 18
x + y = 23
x + 18 = 13
x = 23 - 18
x = 5
******************************
e)
x + y = 25
x - y = 13 (+)
---------------------------
2x = 38
x = 38/2
x = 19
x + y = 25
19 + y = 25
y = 25 - 19
y = 6
********************************
f)
x = 3y
x + y = 100
x + y = 100
3y + y = 100
4y = 100
y = 100/4
y = 25
x = 3y
x = 3.25
x = 75
***************************
g)
x = 2y
x + y = 30
x + y = 30
2y + y = 30
3y =30
y = 30/3
y = 10
x = 2y
x = 2.10
x = 20
*******************************
h)
x + y = 4 (3)
2x - 3y = 3
3x + 3y = 12
2x - 3y = 3 (+)
---------------------
5x = 15
x = 15/5
x = 3
x + y = 4
3 + y = 4
y = 4 - 3
y = 1
********************************************
i)
x + y = 17
6x = 7y + 24
x + y = 17 (7)
6x - 7y = 24
7x + 7y = 119
6x - 7y = 24
-----------------------
13x = 143
x = 143/13
x = 11
x + y = 17
11 + y = 17
y = 17 -11
y = 6
¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨¨
j)
2x + 3y = 19
x - y = - 3 (3)
2x + 3y = 19
3x - 3y = 9 (+)
-------------------------
5x = 28
x = 28
-----
5
x - y = - 3
28 - y = - 3
-----
5
28 - 5y = - 3.5
---------- --------
5 5
28 - 5y = - 15
28 + 15 = 5y
43 = 5y
5y = 43
y = 43
------
5
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