2. System of Equations  2 (or more) equations, each of which has 2 (or more) variables

4. Our goal is normally to find a the values of the variables that work in both equations.

5. In most cases you can think of this as the point where two lines cross. (x,y) is the solution to the system of equations.

6. There are lots of ways to solve systems of equations. One way is by graphing.  Carefully graph both lines on the same axes.  Find the point where they cross.

7. Solve y = 2x + 2 y = x – 1

8. Solve y = 2x + 2 y = x – 1 y = 2x + 2  y-intercept = 2  slope = 2 / 1 y = x – 1  y-intercept = -1  slope = 1 / 1

9. The solution is (3, -4)

10. Solve y = x + 2 y = -x + 4 y = x + 2  y-intercept = 2  slope = 1 / 1 y = -x + 4  y-intercept = 4  slope = -1 / 1

11. The solution is (1,3)

12. Solve x + 2y = 5 2x + y = 4

13. Solve x + 2y = 5 2x + y = 4 Find the intercepts.

14. Solve x + 2y = 5 2x + y = 4 Find the intercepts. x + 2y = 5 (0,2.5)and (5,0) 2x + y = 4 (0,4) and (2,0)

15. The solution is (1,2)

16. Solve 2x + 2y = 6 4x – 6y = 12

17. Solve 2x + 2y = 6 4x – 6y = 12 Intercepts 2x + 2y = 6 (0,3) and (3,0) 4x – 6y = 12 (0,-2) and (3,0)

18. We can tell without even finishing the graph that (3,0) is the solution.

19. Solve 3x + 2y = 12 3x + 2y = 6

20. Solve 3x + 2y = 12 3x + 2y = 6 Intercepts 3x + 2y = 12 (0,6) and (4,0) 3x + 2y = 6 (0,3) and (2,0)

21. These are parallel lines. They both have a slope or -3 / 2. They never intersect, so there is no solution.

22. It’s also possible to have infinitely many solutions, which would mean you have different expressions for the same line. For example:5x + 2y = 10 y = -5 / 2 x + 5

23. There are lots of word problems that involve systems of equations. For instance … Two tacos and a burrito cost $8. One taco and two burritos cost $10. How much is a taco, and how much is a burrito?

24. Two tacos and a burrito cost $8. One taco and two burritos cost $10. How much is a taco, and how much is a burrito? 2t + 1b = 82x + 1y = 8 1t + 2b = 101x + 2y = 10

25. 2x + 1y = 8 1x + 2y = 10 The solution is (2,4)

26. Two tacos and a burrito cost $8. One taco and two burritos cost $10. How much is a taco, and how much is a burrito? (2,4) means a taco costs $2 and a burrito costs $4.