9.3 Solving Systems by Elimination

9.3 Solving Systems by Elimination

based on pages 431-442

Notice the 4x and -4x

They can be "eliminated" when combining the equations together. We do this to solve systems of equations when both are in Standard Form and they have inverse coefficients. (matching but opposite signs)

Notice the -4y and -4y

Here the coefficients match exactly which means they cannot be eliminated yet. We need to multiply one of the equations by -1 first before "eliminating" the y-variables.

Multiple Choice

4x +  8y = 20
-4x + 2y = -30
Which variable will be eliminated?

• The  x
• The  y
• The  z
• The unknown

Multiple Choice

Which variables should be eliminated?

-10x - 2y = 10

2x +2y = 22

• x

• y

• none

Multiple Choice

Solve by elimination:

4x+9y=28

-4x-y=-28

• (-7,0)

• (6,0)

• (-6,0)

• (7,0)

Multiple Choice

Solve by elimination:
-x+2y=17

2x+2y=-10

• ARN
• (-9,4)
• (-9,-4)
• (9,-4)

Multiple Choice

Solve by elimination:
9x-4y=7

x-4y=-17

• (-1,5)
• (-7,5)
• (7,5)
• (3,5)

Poll

How are you feeling about this topic (elimination) so far?

• I understand!

• I need more practice, but I'm getting it

• I do not know where to begin