# Inverse Matrix

• Sep 28th 2008, 04:10 AM
someone21
Inverse Matrix
Need to know the inverse for the matrix (plz teach me the method also not the answer)

-5 -2 -2
2 1 0
1 0 1

it is 3x3 matrix
• Sep 28th 2008, 04:17 AM
mr fantastic
Quote:

Originally Posted by someone21
Need to know the inverse for the matrix (plz teach me the method also not the answer)

-5 -2 -2
2 1 0
1 0 1

it is 3x3 matrix

Why do you need to know? If it's for an assignment or test, you must already have been taught how to do it ....?
• Sep 28th 2008, 04:23 AM
Moo
Hello,

The method in Mr F's link is obviously the best and maybe the simplest...

Here the indigestible direct formula (Rofl) :

If $A=\begin{pmatrix} a&b&c \\ d&e&f \\ g&h&i \end{pmatrix}$

$A^{-1}=\frac{1}{\text{det} A} \begin{pmatrix} ei-fh&ch-bi&bf-ce \\ fg-di&ai-cg&cd-af \\ dh-eg&bg-ah&ae-bd \end{pmatrix}$
• Sep 29th 2008, 02:06 AM
someone21
What do you mean indigest and most importantly, is there any quicker way to find the inverse of the matrix or gauss jordan elimination

So any quicker ways to find the solutions for matrix
• Sep 29th 2008, 02:19 AM
mr fantastic
Quote:

Originally Posted by someone21
What do you mean indigest and most importantly, is there any quicker way to find the inverse of the matrix or gauss jordan elimination

So any quicker ways to find the solutions for matrix

Yes: Use technology.

• Oct 25th 2008, 06:19 AM
someone21
Quote:

Originally Posted by Moo
Hello,

The method in Mr F's link is obviously the best and maybe the simplest...

Here the indigestible direct formula (Rofl) :

If $A=\begin{pmatrix} a&b&c \\ d&e&f \\ g&h&i \end{pmatrix}$

$A^{-1}=\frac{1}{\text{det} A} \begin{pmatrix} ei-fh&ch-bi&bf-ce \\ fg-di&ai-cg&cd-af \\ dh-eg&bg-ah&ae-bd \end{pmatrix}$

Will that indigestible(Wondering) method work in all 3x3 matrix
• Oct 25th 2008, 06:24 AM
mr fantastic
Quote:

Originally Posted by someone21

Will that indigestible(Wondering) method work in all 3x3 matrix

Is matrix A in moo's post a 3x3 matrix? Did moo state any exceptions to the method?
• Oct 25th 2008, 06:32 AM
Moo
Quote:

Originally Posted by mr fantastic
Is matrix A in moo's post a 3x3 matrix? Did moo state any exceptions to the method?

No I didn't state any, but if the matrix is not invertible, that is to say if $det ~ A=0$, then we can talk about an exception (Rofl)
• Oct 25th 2008, 07:31 AM
someone21
Quote:

Originally Posted by Moo
No I didn't state any, but if the matrix is not invertible, that is to say if $det ~ A=0$, then we can talk about an exception (Rofl)

Lol, sorry but what is !!!!det A!!! not yet learned

and how to know that the inverse in not possible, i mean you might think there may be an answer to the matrix and continue solving it with various numbers, So any better ways
• Oct 25th 2008, 12:08 PM
mr fantastic
Quote:

Originally Posted by someone21
Lol, sorry but what is !!!!det A!!! not yet learned

and how to know that the inverse in not possible, i mean you might think there may be an answer to the matrix and continue solving it with various numbers, So any better ways

When you learn about the determinant you will get a method for testing whether the inverse of a given matrix exists. I have already given the general apporach for finding the inverse of a matrix. You can use moo's for a 3x3, if the order is higher you're stuck with with what I've already told you.

It sounds like it might be better if you wait until you've been taught more regarding this subject.