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# matrices - inverse of 3x3 matrix watch

1. does anybody have a method of finding the inverse of a 3x3 matrix?
2. i use by minors. heres how:

A=abc
def
ghi

1- compute A^-1_adj, select a, look at 2x2 matrix not using the row and column of a. so, this is [ef, hi] put the det of this into the place of a. do this for all the other letters. (remember b,d,f,h are negative).
2-transpose the matrix.
done. if u practise this enough, u can possibly do this in one step.
3. (Original post by osiris)
does anybody have a method of finding the inverse of a 3x3 matrix?
Why don't you just use your GDC? Do you have unknown parameters?
For the 'formula' see http://mathworld.wolfram.com/MatrixInverse.html
4. yep i just use my graphical I'm pretty sure in the syllabus it says for finding 3x3 inverses that they expect you to use your calculator.
5. Sylabus details - Core: Matrices:
Content: Inverse matrix: conditions for its existence
Amplifications/Inclusions: Obtaining the inverse of a 3×3 matrix using a GDC.
Exclusions: Other methods for finding the inverse of a 3×3 matrix.
So you do not have to know how to find inverse of 3x3 matrix in other way then by GDC.
And you can still find it on the internet (e.g.: wolfram mathworld)

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