Yet another 'please help me with my math (algebra I) homework' thread

#1
actually, my brother needs help, but i need help helping my brother.
he's got this equation:
-2x+y=-3
4x-2y=6
and he needs to use elimination. any help at all would be greatly appreciated. thanks.
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#2
Multiply the top equation by two, knock out the x's, solve for y.

Is that too simplified?

Well:

-2x+y=-3
4x-2y=6

-4x+2y=-6
4x-2y=6

wait... you've got some bad equations here...

The second one is basically the first one...

EDIT: That's a negative three, my bad. Yeah they've got it below me.
Last edited by Timothym at Feb 7, 2008,
#3
(-2x+y=-3) *2
4x+2y=6

-4x+2y=-6
4x+2y=6

4y=0

y=0

4x-2(0)=6

(4x=6)/4

x=3/2


(3/2, 0)

EDIT: CRAAAAP, i messed up, i read it as 4x+2y=6 instead of 4x-2y=6, my bad

everything cancels out, so they ARE the same line ^. sry, so there are infinite possibilities

(-2x+y=-3) *2
4x-2y=6

-4x+2y=-6
4x-2y=6

0=0
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Last edited by icon_player_5 at Feb 7, 2008,
#4
multiply top equation by 2, then add the two equations, 4y = 0, y = 0. God I miss algebra...
#5
Quote by theking182
actually, my brother needs help, but i need help helping my brother.
he's got this equation:
-2x+y=-3
4x-2y=6
and he needs to use elimination. any help at all would be greatly appreciated. thanks.


-2y=-4x+6
/2 /2

y=-2x+6
maybe?
lol
i attempted the other one, but it pisses me off.
#6
Quote by Timothym
Multiply the top equation by two, knock out the x's, solve for y.

Is that too simplified?


That won't work cause you'll just eliminate everything and get zeroes.

totonEDIT: oh wait I think it will work
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#9
Quote by guitaruboy
i hated learning this in core 3
honestly, do you ever use it in real life unless your a mathmatician (is that even a job?) or a math teacher!


no, you dont

ask any math teacher what application the crap they make you learn has other than math teacher

they will not be able to tell you...
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#11
dont divide by zero!!! *hides under computer chair*
i havent done that in a while but the answer the second guy gave looks right.
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#12
jeez you guys are helpful. thanks a lot!
If man is 5, if man is 5, if man is 5,
then the Devil is 6, then the Devil is 6, then the Devil is 6, the Devil is 6,
And if the Devil is 6,

then God is 7, then God is 7, then God is 7
This monkey's gone to heaven.
#13
Quote by guitaruboy
i hated learning this in core 3
honestly, do you ever use it in real life unless your a mathmatician (is that even a job?) or a math teacher!

well you'll need to know this stuff for the SAT or other standardized tests, and they help determine whether or not you get into the college of your choice.
Also, this is just basic algebra. You probably will end up using this. Wait until you start doing calculus. THEN you can make those "i'll never need this" arguments..
#14
-2x+y=-3
4x-2y=6

x=1
y=-1

And algebra is actually pretty practical. Sure, you don't get presented with a problem like this but you'll use it a bit someday.
#15
Quote by a4lrocker
dont divide by zero!!! *hides under computer chair*
i havent done that in a while but the answer the second guy gave looks right.


It's not though, check his signs... he made the second y value a positive as compared to a negative. Thus, it adds out fine. In the true problem, the values will always completely cancel as tipp or whomever said above.
#16
Quote by rush5757
well you'll need to know this stuff for the SAT or other standardized tests, and they help determine whether or not you get into the college of your choice.
Also, this is just basic algebra. You probably will end up using this. Wait until you start doing calculus. THEN you can make those "i'll never need this" arguments..


i know! we already did it and its horrible!
#17
Quote by guitaruboy
i hated learning this in core 3
honestly, do you ever use it in real life unless your a mathmatician (is that even a job?) or a math teacher!

Ya I use algebra and trig almost daily at work. Well a couple time a week anyways.
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#18
Dude...it's algebra one. All you're learning are basic processes that you use to solve bigger, more "real" applications later.

If you ever take Calculus, you'll see what I mean. Lot's of business applications, as well as engineering, piloting, boating, cartographing (word?), loads of them.
#19
-2x+y=-3
4x-2y=6

y=2x-3

4x-2(2x-3)=6
4x-(4x-6)=6
6=6

Wait... those two equations are the same. The bottom one is just the top one multiplied by -2.
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#20
-2x+y=-3
4x-2y=6

Multiply top equation by 2. Then you can eliminate the y.

-4x=-6
4x=6

Then you are able to just use addition, so add the numbers straight down and you get this:

0=0

This means there is infinitely many solutions.
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#21
Quote by theking182
actually, my brother needs help, but i need help helping my brother.
he's got this equation:
-2x+y=-3
4x-2y=6
and he needs to use elimination. any help at all would be greatly appreciated. thanks.



What book does your brother use? I swear I had that exact same problem three days ago...

Anyway, multiply the top by 2 so it ends up as:

-4x + 2y= -6
4x - 2y = 6

then choose one variable to cancel out (let's cancel out y. You can do this because you are essentially adding the two equations together, and a -y + y would equal 0) so it ends up as:

0 = 6

if your book is the same as mine, you'd be on the "linear exceptions" part and the answer is no solution.
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#23
So I assume "elimination" implies that the point is to prove that the two equations are equivalent by manipulating and adding to one another until you are left with 0?

Very simple...multiply the first eq. by 2 and add to the second equation.

Edit: I see, you are trying to find x and y?! You can't solve for x and y if you only have one equation (which is essentially what you have)

Nevermind a long explanation for why math is necessary in life. Just remember technical career (basically almost any interesting career to me ) will require deep understand of math.
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Last edited by pyrochris at Feb 8, 2008,
#24
-2x+y=-3
4x-2y=6

2 [-2x+y=-3]

-4x + 2y = -6
4x - 2y = 6
--------------------
0x + 0y = 0
0 = 0

Edit: Therefore, you have an infinite number of solutions.
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#25
^^^ I should have remembered that from matrix algebra! The Infinite solutions part I mean . It is perfectly intuitive once you graph it out and consider that (that particular) equation represents a line in space, and any point on that line is solution.
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#26
You have a null matrix there I think. I couldn't be arsed to check.
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#27
it can be put into a matrix but to solve by elimination do what they have been doing but only one guy has said the correct answer..... no solution
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#28
Quote by youngandplayin
it can be put into a matrix but to solve by elimination do what they have been doing but only one guy has said the correct answer..... no solution


either my maths book is wrong or that sum has infinite solutions