Solve the systems of equations in numbers 1 – 9 using substitution. Show your work.

1. y = (2/3)x - 1
y = -x + 4

2. x + y = 0
3x + y = -4

3. 4x + 3y = -15
y = x + 2

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

5. y = 2x
x + y = 3

6. x = 3 - 3y
x + 3y = -6

7. y = -2x + 1
y = x - 5

8. y = (1/2)x - 3
y = (3/2)x – 1

9. x + y = 2

4y = -4x + 8

Solve numbers 10 – 18 using the elimination method. Show your work.

10. y = (2/3)x - 1
y = -x + 4

11. x + y = 0
3x + y = -4

12. 4x + 3y = -15
y = x + 2

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

14. y = 2x
x + y = 3

15. x = 3 - 3y
x + 3y = -6

16. y = -2x + 1
y = x - 5

17. y = (1/2)x - 3
y = (3/2)x – 1

18. x + y = 2

4y = -4x + 8

19. Why are the substitution and elimination methods necessary when we already know how to solve systems of linear equations using the graphing method?