Răspuns:
a)
x + y = -2 => x = -2 - y
x - y = 4
-2 - y - y = 4
-2y = 6
y = -3
x = -2 + 3
x = 1
b)
3x + y = 7 => y = 7 - 3x
2x - y = 8
2x - (7 - 3x) = 8
2x - 7 + 3x = 8
5x = 8 + 7
5x = 15
x = 3
y = 7 - 3(3)
y = 7 - 9
y = - 2
c)
x = 2y
2x + 3y = 4
2(2y) + 3y = 4
4y + 3y = 4
7y = 4
y = 4/7
x = 2(4/7)
x = 8/7
d)
x - 2y = 3 => x = 3 + 2y
x + y = - 4
3 + 2y + y = -4
3y = -4 - 3
3y = -7
y = -7/3
x = 3 + 2(-7/3)
x = 3 - 14/3
e)
2x + y = 1 => y = 1 - 2x
x - y = -4
x - (1 - 2x) = -4
x - 1 + 2x = -4
3x = -4 + 1
3x = -3
x = -1
y = 1 - 2(-1)
y = 1 + 2
y = 3
f)
x = 5
x + y = 7
5 + y = 7
y = 7 - 5
y = 2
g)
-2x + y = 5
x - y = -1 => x + 1 = y
-2x + x + 1 = 5
-x = 5 - 1
-x = 4
x = -4
i)
[tex] \frac{x}{3} = \frac{y}{1} [/tex]
x = 3y
10x - 3y = -1
10(3y) - 3y = -1
30y - 3y = -1
27y = -1
y = -1/27
x = 3(-1/27)
x = -1/9
j)
y = 3x
2x + y = 3
2x + 3x = 3
5x = 3
x = 3/5
y = 3(3/5)
y = 9/5
