# Inverse of a Matrix: Solve for m, n, p

• May 15th 2011, 08:39 AM
Dug
Inverse of a Matrix: Solve for m, n, p
m+2n+p=5
3m+4n+p=8
m-6n+2p=4

There are 2 ways taught us to solve for this using matrix.
The Inverse method and Row-Echelon method.
In row echelon method i got this answer:

m=1
n=1/2
p=3

i know the answer is correct because when i substitute it to the equations above, i get the correct answer.

(1)+2(1/2)+(3)=5
3(1)+4(1/2)+(3)=8
1-6(1/2)+2(3)=4

My problem is, when I use the Inverse method, i get the determinant -18, and the rest of the process gives me a wrong answer.
• May 15th 2011, 08:52 AM
Quacky
I agree with your determinant. Can you post the rest of your working?
• May 15th 2011, 09:10 AM
Dug
• May 15th 2011, 09:18 AM
Quacky
Quote:
Looks to me like there are some substantial sign errors. I think you're trying to do too much at once.
I think the matrix of cofactors should be:
14 -5 -22
-10 1 8
-2 2 -2

Edit: I've just made a correction.
• May 15th 2011, 09:26 AM
Dug
Quote:

Originally Posted by Quacky
Looks to me like there are some substantial sign errors. I think you're trying to do too much at once.
I think the matrix of cofactors should be:
14 -5 -22
-10 1 8
-2 2 -2

Edit: I've just made a correction.

wow i feel stupid. thanks! i got the correct answer now :)