#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.

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.

#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.

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

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

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 badeverything 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

*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

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

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

#7

God I miss algebra...

+1

#8

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!

honestly, do you ever use it in real life unless your a mathmatician (is that even a job?) or a math teacher!

#9

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...

#10

the only way to do it is by inspection as far as i know... my ALG I teacher showed us this as a trick question back in the day.

By inspection, x=1 and y =-1.

By inspection, x=1 and y =-1.

#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.

i havent done that in a while but the answer the second guy gave looks right.

#12

jeez you guys are helpful. thanks a lot!

#13

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.

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

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

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

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.

#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.

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.

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.

#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.

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.

#21

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.

#22

elimination is so easy, its my favorite out of the three methods

#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.

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.

*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.

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.

#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.

#26

You have a null matrix there I think. I couldn't be arsed to check.

#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

#28

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