Solving systems of equations by elimination

koffii71

New member
I have a problem on -2x-9y=-25
-4x-9y=-23

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stapel

Super Moderator
Staff member
I have a problem on -2x-9y=-25
-4x-9y=-23
Where are you stuck? You did the obvious subtraction, and... then what?

koffii71

New member
I have to eliminate the number that has the opposite sign

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koffii71

New member
Thanks

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stapel

Super Moderator
Staff member
I have to eliminate the number that has the opposite sign
Okay; you're wanting to add instead of subtract. That's fine. You multiplied one of the equations by -1 to create the opposite-sign terms and... then what?

Bob Brown MSEE

Full Member
By Elimination?

I have a problem on -2x-9y=-25
-4x-9y=-23

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From the first equation get 9y = 25-2x
Then "eliminate" the 9y in the second equation, by replacing
9y with (25-2x)

You will then be able to solve for x

stapel

Super Moderator
Staff member
From the first equation get 9y = 25-2x
Then "eliminate" the 9y in the second equation, by replacing....
FYI: In many ("most"?) books, this replacement, being a substitution, is called the method of substitution. "Elimination" means "setting up the equations so you can add down and eliminate one of the variables".

Bob Brown MSEE

Full Member
Correction

FYI: In many ("most"?) books, this replacement, being a substitution, is called the method of substitution. "Elimination" means "setting up the equations so you can add down and eliminate one of the variables".
Oh, Yes,
You are right. I believe 100%. Especially in the context of Augmented Matrices.

Adding equals to equals with the intent to eliminate, in the algebraic context.
Thanks for the correction

The method that I used is indeed called substitution.

skyler

New member
solving systems of equations using elimination

my problem on -9x+6y=6
-10x+8y=20

i need help on how to work this problem out anyone plz help