1. ## Inverse Matrix help!

Can someone explain how you do inverse matrices with a 2X2 and 3X3 matrix? Please.
Here are two problems and I don't know how to get the answers.

R1 is -1 -2
R2 is 3 4

the 3X3 is
R1 is 1 0 1
R2 2 1 3
R3 -1 1 1

TIA!

2. assuming you know how to transpose a matrix and fin the determinant:

inverse of 2x2 matrix is 1/determinant[matrix transposed]

3. Originally Posted by djmccabie
assuming you know how to transpose a matrix and fin the determinant:

inverse of 2x2 matrix is 1/determinant[matrix transposed]

Hi, I don't think that is correct. My book says that A is NOT = to 1/A because A is a matrix and not a number

4. The answer for the first one is (its in the back of the book and I don't know how to do it.)

R1 is 2 1
R2 -1.5 -.5

5. Originally Posted by scottydoint
Can someone explain how you do inverse matrices with a 2X2 and 3X3 matrix? Please.
Here are two problems and I don't know how to get the answers.

R1 is -1 -2
R2 is 3 4

the 3X3 is
R1 is 1 0 1
R2 2 1 3
R3 -1 1 1

TIA!

2x2 matrix
detA = (top left)(bottom right)-(top right)(bottom left)
detA = -4 - (-6)
detA = 2

matrix transposed = 4 -3
2 -1

so inverse = 1/2[4 -3]
[2 -1]

do you need the 3x3 matrix explained?

6. arghhh now times what i just did by the original matrix! lol im useless

7. ok, I kinda get it now. can you do the 3X3 please.

8. does it work? i dont seem to get the answer in the book? its gettin late in the uk lol.

3x3 matrix

first find the determinant.

R1 is 1 0 1
R2 2 1 3
R3 -1 1 1

this is 1(1-3)-0(-3-2)+1(2--1)
=-2-0+3
=1

Now find all the minor determinants of each element.

R1 -2 0 3
R2 -1 2 1
R3 -1 1 1

then add a minus sign to each of the even numbered elements.

R1 -2 -0 3
R2 +1 2 -1
R3 -1 -1 1

Transpose the matrix

R1 -2 1 -1
R2 0 2 -1
R3 3 -1 1

now multiply by the 1/determinant found at the beginning

1 * New Matrix

hope this helps,

more importantly i hope this is right lol