SOLUTION: 3x-y=21 2x+y=4 Describe a first step for solving each system using elimination. then solve each system.

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Question 35917This question is from textbook Prentice Hall Algebra Tools For A Changing World
: 3x-y=21
2x+y=4
Describe a first step for solving each system using elimination. then solve each system. This question is from textbook Prentice Hall Algebra Tools For A Changing World

Answer by tran3209(100) About Me  (Show Source):
You can put this solution on YOUR website!
The two equations:
3x-y=21
2x+y=4
Step 1.
Solve for one of the varriables first.Simplfy the equation.
2x+y=4
subtract 2x from both sides
y=-2x+4
You now know what "y" is equal to.
Next you will plug what "y" equals into the first equation( 3x-y=21)
So the new equation would look like this:
3x+2x-4=21
5x=25
x=5
Now find out what "y" equals.
y=-2x+4
y=-10+4
y=-6
The Check Step.
You now know that y=-6 and x=5
You will plug the numbers back into the first or second equation.
3x-y=21
3(5)-(-6)=21
15+6=21
21=21