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Fellow ATOT'ers, i need help with some math! any volunteers? :)

W

WarDemon666

Platinum Member
Hey everyone,

Heres the question:

find the inverse of:
125
014
326

heres what i got so far and im stuck:
i did:
3*r1-r3, 4*r2-r3 and im here:
125|1 0 0
014|0 1 0
007|(-3)4(-1)

any help would be apprechiated!
 
Originally posted by: Howard
Originally posted by: WarDemon666
42? how 42?

Im supposed to get 6 numbers no?

Could you explain how you got that? Thanks
Click to expand...
He's just kidding. But don't you mean 9 numbers?
Click to expand...

typo 😱 heheh.... 😛

Didnt learn cofactor expansion yet... we do it with the identity on the side
 
Originally posted by: WarDemon666
I googled, couldnt understand the explanations, none of the sites i found are like we do in class
Click to expand...
Book: Hitchhikers Guide to the Galaxy. Basicly, an advanced civilization (hmmm...) asks a super computer what the answer to life, the universe, and everything is. The answer given after much processing time, is 42.

You really need to get out more 😛
 
multiply row 2 * (-2) and add to row 1
divide row 3 by 7, then multiply by (-4) and add to row 2
multiply row 3 by -5, then add to row 1
you should have the identity matrix on the left, and the inverse on the right

basic idea is to augment the identity matrix to the original matrix, then get the identity matrix on the left, and the inverse will be on the right
 
Originally posted by: sleepmachine
multiply row 2 * (-2) and add to row 1
divide row 3 by 7, then multiply by (-4) and add to row 2
multiply row 3 by -5, then add to row 1
you should have the identity matrix on the left, and the inverse on the right

basic idea is to augment the identity matrix to the original matrix, then get the identity matrix on the left, and the inverse will be on the right
Click to expand...

Thanks im doing it right now, see what happens
 
umm, sleepmachine: did you start from scratch, or from where I finished? Cause it doesnt seem to work from where i finished..
 
from where you finished.

maybe it'll be easier if you divide the third row by 7, then zero out everything above the 1's on the diagonals.
 
Do these step by step to see it better
-3r1 + r3
-2r2 + r1
edit 4r2 + r3
(1/7)r3
3r3 + r1
-4r3 + r2

should give:
-2/7 -2/7 3/7
12/7 -9/7 -4/7
-3/7 4/7 1/7
 
Originally posted by: hscorpio
Do these step by step to see it better
-3r1 + r3
-2r2 + r1
edit 4r2 + r3
(1/7)r3
3r3 + r1
-4r3 + r2

should give:
-2/7 -2/7 3/7
12/7 -9/7 -4/7
-3/7 4/7 1/7
Click to expand...

ah ha,... that helps. I was stuck... will try again..

Thanks!!!!!
 
how do you come up with these numbers though? Where do they come from?

I dont understanndd 🙁
It works though, im going to try doing it again without your instructions.. wonder if that would help
 
What class is this from?
You might want to google around for Gauss Jordan Elimination for more info.
edit also search for "elementary row operations".

Basically you want to start by getting 1 in the upper left. Then get 0's below the one. Now move to the next column and get 1 in the second row. Then get the 0's above and below. Then repeat this for each column so you make the identity matrix.

This Gauss-Jordan elimination stuff is very useful for solving large systems of equations, but I do it all on my calculator now since it saves loads of time.



 
edit: mathematics 1 class

were doing the elementary row operations, i just remembered. didnt tihnk of googling that....

Ill check it out..

Heres another question im stuck on:

26-4
013
-1-32

doesnt seem to have one? could this be true? im stuck...

can someone go through it for me please?

Thanks a lot
 
Originally posted by: WarDemon666
edit: mathematics 1 class

were doing the elementary row operations, i just remembered. didnt tihnk of googling that....

Ill check it out..

Heres another question im stuck on:

26-4
013
-1-32

doesnt seem to have one? could this be true? im stuck...

can someone go through it for me please?

Thanks a lot
Click to expand...

Ok i figured out that

row 3 is -1/2 of row 1, which means they areeeeeeeeeeeee: ??? Can i just say it directly? or do i have to go through it to say theres no inverse?

Any ideas?
 
26-4
013
-1-32

There is no inverse of this matrix.

Before going through the hassle of trying to find the inverse you should always check that the determinant of the matrix is not equal to zero. If det(A)=0 then the inverse of A does not exist.
 
oh!! thats ac-bd = ? or soemthing like this?

Im reading about elementary row operations,, its actually really really helping. A LOT. thanks hscorpio
 
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