- Thread starter koffii71
- Start date

- Joined
- Feb 4, 2004

- Messages
- 15,943

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

-4x-9y=-23

Please be complete. Thank you!

- Joined
- Feb 4, 2004

- Messages
- 15,943

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?I have to eliminate the number that has the opposite sign

- Joined
- Oct 25, 2012

- Messages
- 594

Your question asked how to use elimination.I have a problem on -2x-9y=-25

-4x-9y=-23

Sent from my SGH-T889 using Tapatalk

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

- Joined
- Feb 4, 2004

- Messages
- 15,943

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".Your question asked how to use elimination.

From the first equation get 9y = 25-2x

Then "eliminate" the 9y in the second equation, by replacing....

- Joined
- Oct 25, 2012

- Messages
- 594

Oh, Yes,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".

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.