Systems of Equations by Elimination

If a system of linear equations has one solution, what does this mean about the two lines? 

• Parallel lines
• the same line 
• Intersecting lines

What is the best first step to solve this system by elimination?

• Add the equations to eliminate y

• Subtract the equations to eliminate y

• Multiply the second equation by 3.

• Multiply the first equation by 2

Solve by elimination:
-9x-4y=-20

5x+4y=4

• (-4,4)
• (4,4)
• (4,-4)
• (-4,-4)

Solve by elimination:
7x+y=-9

-3x-y=5

• No solution
• (1,8)
• (-2,-3)
• (-1,-2)

Solve by elimination:
4x+9y=28
-4x-y=-28

• (-7,0)
• (6,0)
• (-6,0)
• (7,0)

Solve using elimination. 
 4x + 8y = 20
-4x + 2y = -30

• (-7,1)
• (2,-5)
• (-2,5)
• (7,-1)

Solve by elimination
-6x + 5y = 1
6x + 4y = -10

• (1,-1)
• (0,-1)
• (1,1)
• (-1,-1)

 Solve using elimination.  7x + 2y = 24  

-8x - 2y = -30

• (6,-9)

• (-9,6)

• No solution

• Infinite number of solutions

Solve the following system by using elimination:

3x - 5y = 8

2x + 5y = -3

• (1, 5)

• (1, -1)

• (-1, -1)

Solve by elimination: -7x+9y=-29

7x+2y=-15

• (-4,-1)

• (-1.-4)

• (-1,4)

• (-1,6)