Systems of Equations 3x3's - Cool math Algebra Help Lessons

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Coolmath Algebra
Systems of Equations 3x3's Lesson 2 - Solving by Elimination
(page 5 of 8)
---- This algebra lesson explains how to solve a system of 3 equations and 3 unknowns by the elimination (addition) method.

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STEP 2: Use

and

to ditch the y:

1 ) ( 2x - y + 5z = 4 ) ( 2 ) and 3 ) -3x + 2y - 6z = -7 ... add them together ... ( 4x - 2y + 10z = 8 ) + ( -3x + 2y - 6z = -7 ) = x + 4z = 1 ... put a box around this equation

Now, look at the two boxed guys... Those are our 2 x 2's! These will give us the values for x and z...

STEP 3: Solve the 2 x 2... ditch the x:

( 3x + 6z = 3 ) + ( -3x - 12z = -3 ) = ( -6z = 0 ), which gives z = 0 ...circle him since it's one of our answers!

Now substitute z = 0 into one of the 2 x 2 guys to get x:

x + 4z = 1 ... x + 4 ( 0 ) = 1 ... x = 1 ... circle him

Continued on the next page

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