Desperate need of Algebra 2 help

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10-20-2009, 05:42 PM
Alysser

Desperate need of Algebra 2 help

I seriously don't get anything I am learning right now. I paid attention to the notes, but honestly, I just don't even get where to start. We are learning

SOLVING LINEAR SYSTEMS WITH THREE VARIABLES. DOES anyone KNOW how do this? It's for extra credit, which I need so desperately :( I have been trying to understand this for an hour with videos one youtube and it's not working at all :/ I am going to try again. If someone could teach me with one problem clearly I can probably get it. Here's a problem

8x + 2y - Z = -25
3x - 3y + 5z = 10
-5x + 6y - 2z = 17

If no one gets it I understand, Cause I certainly don't but this is worth a try posting. Thanks in advance.
10-20-2009, 05:52 PM
caseysmom

My kid will know, when she gets home (from math tutoring) in an hour I will have her help you if nobody else has. I can even have her call you if necessary...you are siblings you know :)
10-20-2009, 08:44 PM
Daisy and Delilah

Please post the answer. I am so rusty on this but I have a guess.:confused: I can't wait. :)
10-20-2009, 08:49 PM
Alysser

I still haven't found it, I gave up on them, I can't get it AT ALL. My friend is helping me with them tomorrow morning hopefully. :( Hehe, thanks mom! Always trying to help - It'd be great if my "sister" could help me out.
10-20-2009, 08:49 PM
caseysmom

My daughter started replying and then she got frustrated, she hasn't had algebra 2 since she was a freshman so she is rusty also.

She may come back and finish her reply later..
10-20-2009, 08:53 PM
Alysser

Quote:

Originally Posted by caseysmom

My daughter started replying and then she got frustrated, she hasn't had algebra 2 since she was a freshman so she is rusty also.

She may come back and finish her reply later..

Tell her thank you for me! Thanks for trying to help, because I don't even get it at all. I appreciate any effort. I am a junior in Algebra 2, shows how smart I am :eek:
10-20-2009, 08:55 PM
caseysmom

Well it must be hard because she is a math wiz...she drafted an answer but she isn't sure its rights...i'm tempted to send it behind her back:D
10-21-2009, 06:55 AM
Riptide

Maybe this will help?

http://www.coolschool.ca/lor/PMA11/unit5/U05L06.htm
10-21-2009, 07:15 AM
smokey the elder

I tried solving it as a matrix but linear algebra was over 30(!) years ago and I stunk on ice at it then! Good luck.
10-21-2009, 03:32 PM
emily_the_spoiled

If I remember correctly it is something like this...

1) equation 1 (8x + 2y - Z = -25 ) solve for X (you will end up with a Y and a Z in the answer))

2) substitute the answer from step 1 into equation 2 (3x - 3y + 5z = 10) and solve for Z (you will end up with a Y in the answer but no X)

3) substitute the Z answer from the previous steps into equation 3 (-5x + 6y - 2z = 17) and solve for Y ( you will end up with an X in the answer but no Z)

4) substitute the answer from step 2 and 3 in to equation 1, solving for X. This time you will get a numerical answer. Then you can solve for the remaining variables based on the answers from step 2 and 3.

Good luck!
10-21-2009, 03:36 PM
Barbara

Quote:

Originally Posted by Alysser

8x + 2y - Z = -25
3x - 3y + 5z = 10
-5x + 6y - 2z = 17

Take the first equation and multiply it by 5:
5*(8x + 2y -z)= 5*(-25)
40x + 10y-5z=-125
Then add it to equation #2
40x +3x +10y-3y-5z+5z= -125+10
43 x +7y= -115

Then take the first equation and multiply it by -2
-2*(8x +2y -z)= -2*(-25)
-16x -4y +2z =50

Add it to equation #3
-16x -5x -4y +6y +2z -2z=17+50
-21x +2y= 67

Now you have two equations left with only x and y:
43x + 7y =-115
-21 x +2y=67

From the second equation you get
2y=21x+67

y= (21x +67)/2 ((We call this equation A as I'll need it in a second))

Put this in the first equation

43x + 7/2(21x+67)=-115

43x +7*21x/2 +7*67/2=-115

I hope you are better in calculating these numbers than I am because while I can do the math I make plenty of faults when calculating numbers. When in school I always got results like that - e.g. I can see that 7*21/2 will by no means be a nice number like 4 or even 15. So I hope I get the numbers right;)

43x + 73,5x +234,5 =-115
116,5 x =-349,5
x=-349,5/116,5
x=-3

Now we go back to equation A:
y=(21x +67)/2
y=(21*(-3)+67)/2
y=(-63+67)/2
y=4/2
y=2

Now we could go back to any of the first equations but I suppose #1 will be easiest.
8x + 2y - Z = -25
You bring the z to one side:
z=8x+2y+25
z=8*(-3)+2*2+25
z=-24+4+25
z=5

I suppose it is right as all the results are nice and clean ;)

That was fun. Math for me is also 30 years ago but it was my favorite ;)
10-21-2009, 04:37 PM
lvpets2002

:) Good Luck Kidos.. Hey I stunk at it then & know I am plum dumb with it now.. I have been out of school for over 33 years.. However reading your post are making my head spin..
10-21-2009, 06:42 PM
Alysser

THANK you guys so much for your help!! SOO much, I kinda get this a little better now :D THANK YOU! Barbara, thanks so much for the step by step info and showing the work. This is exactly what I needed :) Thanks so much, you guys are the best :)
10-22-2009, 06:45 PM
lizbud

Quote:

Originally Posted by Barbara

Take the first equation and multiply it by 5:
5*(8x + 2y -z)= 5*(-25)
40x + 10y-5z=-125
Then add it to equation #2
40x +3x +10y-3y-5z+5z= -125+10
43 x +7y= -115

Then take the first equation and multiply it by -2
-2*(8x +2y -z)= -2*(-25)
-16x -4y +2z =50

Add it to equation #3
-16x -5x -4y +6y +2z -2z=17+50
-21x +2y= 67

Now you have two equations left with only x and y:
43x + 7y =-115
-21 x +2y=67

From the second equation you get
2y=21x+67

y= (21x +67)/2 ((We call this equation A as I'll need it in a second))

Put this in the first equation

43x + 7/2(21x+67)=-115

43x +7*21x/2 +7*67/2=-115

I hope you are better in calculating these numbers than I am because while I can do the math I make plenty of faults when calculating numbers. When in school I always got results like that - e.g. I can see that 7*21/2 will by no means be a nice number like 4 or even 15. So I hope I get the numbers right;)

43x + 73,5x +234,5 =-115
116,5 x =-349,5
x=-349,5/116,5
x=-3

Now we go back to equation A:
y=(21x +67)/2
y=(21*(-3)+67)/2
y=(-63+67)/2
y=4/2
y=2

Now we could go back to any of the first equations but I suppose #1 will be easiest.
8x + 2y - Z = -25
You bring the z to one side:
z=8x+2y+25
z=8*(-3)+2*2+25
z=-24+4+25
z=5

I suppose it is right as all the results are nice and clean ;)

That was fun. Math for me is also 30 years ago but it was my favorite ;)

Wow, Barbara, color me impressed.:) Math was never my strong suit.:)
10-22-2009, 07:34 PM
RICHARD

That is the thing that rocks about PT.

I started to look at Barbara's work then said some dirty words......
Who cares about the answers!

I want to know how long she took to type it all out!:D

---------------------

I just finished watching a documentary about the IMO of 2006.

http://www.unl.edu/amc/e-exams/e9-im...pictures.shtml

I think I am more impressed by the geniuses we have in house here at PT.:D
10-22-2009, 08:06 PM
slick

Quote:

Originally Posted by Barbara

Take the first equation and multiply it by 5:
5*(8x + 2y -z)= 5*(-25)
40x + 10y-5z=-125
Then add it to equation #2
40x +3x +10y-3y-5z+5z= -125+10
43 x +7y= -115

Then take the first equation and multiply it by -2
-2*(8x +2y -z)= -2*(-25)
-16x -4y +2z =50

Add it to equation #3
-16x -5x -4y +6y +2z -2z=17+50
-21x +2y= 67

Now you have two equations left with only x and y:
43x + 7y =-115
-21 x +2y=67

From the second equation you get
2y=21x+67

y= (21x +67)/2 ((We call this equation A as I'll need it in a second))

Put this in the first equation

43x + 7/2(21x+67)=-115

43x +7*21x/2 +7*67/2=-115

I hope you are better in calculating these numbers than I am because while I can do the math I make plenty of faults when calculating numbers. When in school I always got results like that - e.g. I can see that 7*21/2 will by no means be a nice number like 4 or even 15. So I hope I get the numbers right;)

43x + 73,5x +234,5 =-115
116,5 x =-349,5
x=-349,5/116,5
x=-3

Now we go back to equation A:
y=(21x +67)/2
y=(21*(-3)+67)/2
y=(-63+67)/2
y=4/2
y=2

Now we could go back to any of the first equations but I suppose #1 will be easiest.
8x + 2y - Z = -25
You bring the z to one side:
z=8x+2y+25
z=8*(-3)+2*2+25
z=-24+4+25
z=5

I suppose it is right as all the results are nice and clean ;)

That was fun. Math for me is also 30 years ago but it was my favorite ;)

Ahhhh, yeah....what she said!!! :confused::confused: Barbara, you never cease to amaze me. I really don't have a clue what you are talking about, but it sure sounds good! :D
10-23-2009, 03:04 AM
Barbara

Quote:

Originally Posted by RICHARD

I want to know how long she took to type it all out!:D

Like 20 minutes? After finding that in the first try I had only multiplied the left hand of the equation and in the second try I had multiplied 5*25= 50:D:p
10-23-2009, 12:15 PM
smokey the elder

Wow! That's great. I remembered that you needed to get down to two equations in terms of x and y, but got stuck after that!:D
10-23-2009, 01:52 PM
Daisy and Delilah

I am alot more rusty than I thought. Awesome!!! :eek: :eek: :eek: