# Solve Systems by Graphing - *Coach Campbell*

Objective The student will be able to: solve systems of equations by graphing. SOL: A.4e Designed by Skip Tyler, Varina High School What is a system of equations? A system of equations is when you have two or more equations using the same variables. The solution to the system is the point

that satisfies ALL of the equations. This point will be an ordered pair. When graphing, you will encounter three possibilities. Intersecting Lines The point where the lines intersect is your solution. The solution of this graph is (1, 2) (1,2)

Parallel Lines These lines never intersect! Since the lines never cross, there is NO SOLUTION! Parallel lines have the same slope with different y-intercepts. 2

Slope = = 2 1 y-intercept = 2 y-intercept = -1 Coinciding Lines These lines are the same! Since the lines are on top of each other, there are INFINITELY MANY SOLUTIONS! Coinciding lines have the

same slope and y-intercepts. 2 Slope = = 2 1 y-intercept = -1 What is the solution of the system graphed below? 1. 2. 3.

4. (2, -2) (-2, 2) No solution Infinitely many solutions 1) Find the solution to the following system: 2x + y = 4 x-y=2 Graph both equations. You can graph using x- and yintercepts (plug in zeros), or you can change the equation to slope-intercept form (solve for y).

2x + y = 4 xy=2 Graph the line using the ordered pairs or equation of the line. Graph the equations. 4 Where do the lines intersect? (2, 0)

y= x-y=2 -x -x -y= -x+2 -1 -1 y= x-2 + 2x 2x + y = 4

2x + y = 4 2(2) + (0) = 4 x-y=2 (2) (0) = 2 Nice joblets try another! 2) Find the solution to the following system: y = 2x 3 -2x + y = 1 Graph both equations. Put both equations in slope-intercept form. y = 2x 3

y = 2x + 1 Graph using slope and y-intercept Graph the equations. y = 2x 3 m = 2 and b = -3 y = 2x + 1 m = 2 and b = 1 Where do the lines intersect? No solution! Notice that the slopes are the same with different y-intercepts. If you recognize this early, you dont have to graph them!

Check your answer! Not a lot to checkJust make sure you set up your equations correctly. I double-checked it and I did it right What is the solution of this system? 3x y = 8 2y = 6x -16 (3, 1) 2. (4, 4) 3. No solution 4. Infinitely many solutions

1. Solving a system of equations by graphing. Let's summarize! There are 3 steps to solving a system using a graph. Step 1: Graph both equations. Graph using slope and y intercept or x- and y-intercepts. Be sure to use a ruler and graph paper! Step 2: Do the graphs intersect?

This is the solution! LABEL the solution! Step 3: Check your solution. Substitute the x and y values into both equations to verify the point is a solution to both equations.

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