Posted by Mathew on Thursday, January 13, 2011 at 8:55pm.
2x + y = -5
3x +5y = 3
How come I have to multiply by 5 to make the y variables cancel, like what does that mean? I don't get how ur supposed to multiply like where and how? Im really stuck right now, please help:(
- Necessary Math HELp - helper, Thursday, January 13, 2011 at 9:21pm
2x + y = -5
3x +5y = 3
to solve 2 equations simultaneously (at the same time), by elimination, the object is to get rid of one variable.
adding a negative to a positive equals zero, for example, 5y + -5y = 0.
So, to get rid of y in the above 1st equation, since the first equation has just "y" and the second equation has "5y", you multiply the first equation by -5 to get "-5y" so that the -5y added to 5y = 0,
Multiply the whole equation by -5
-5 (2x + y = -5) = -10x - 5y = 25
Now add the two equations together
-10x - 5y = 25
3x + 5y = 3
-7x + 0 = 28
-7x = 28
x = -4
substitute x = -4 in either equation and solve for your y value
do you understand this?
- Necessary Math HELp - Mathew, Thursday, January 13, 2011 at 9:28pm
Thanks a lot buddy, I really appreciate all the time you put to help me with my question. Yeah thanks to your explanation I get it, thanks a lot:)
So here's how I substitute right?
2x+y = -5
2(-4)+y = -5
-8 +y = -5
Then I add 8 to both sides and get:
y = -3
Therefore the solution would be:
- Necessary Math HELp - helper, Thursday, January 13, 2011 at 9:32pm
correct, the answer is (-4, 3)
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