Inconsistent or dependent system of equations

Solve the system of linear equations. If the unique solution does not exist state weather the system is inconsistent or dependent.

1. -x - y = 4
x -y = -8

2. 3x - 2y = 23
x +5y = -15

3. 4x + 2y = 4
y = 2 - 2x

4. 4x - 3y = 9
2x + y = 12

5. 5x + 4y = 40
x + 2y = 11

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...= 23 -------------(i)
x +5y = -15 --------------(ii)
Multiply equation (ii) by 3, we will get
3x + 15y = -45 ----------(iii)
Subtract (i) from (iii), we will get
17y = -68
Divide each side by 17, we will get
 y = -4
Substitute value of y in (ii), we will get
x + 5(-4) = -15
x - 20 = -15
=> x = -15 + 20 = 5
The solution is x = 5, y = -4

3. 4x + 2y = 4
y = 2 - 2x ...