# Linear algebra A' is A when two of A lines switched,A Invertible prove (A+A')x=0

linear algebra A' is A when two of A lines switched,A Invertible prove (A+A')x=0....

## Homework Statement

A is a n*n matrix
A' is the matrix A when two two lines i,j are switched.
(switch two random lines is A and you get A')
If A Invertible Prove that the system (A+A')x=0 has infinite solutions

## Homework Equations

linear algebra including Determinant

## The Attempt at a Solution

Well I know that A+A' has two identical lines so when subtracting them I get a line of 0 and then Because I know there is a line of 0 I know that there are infinite solutions...
But I did not used the fact that A is Invertible...
How do I solve it while using this fact? , I try to use Determinant but I do not mange to.
Thank you.

## Answers and Replies

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let Det(A)=k
then Det(A')=-k (two rows are switched)

Det(A+A')=?

Thank you very much

Dick
Homework Helper

let Det(A)=k
then Det(A')=-k (two rows are switched)

Det(A+A')=?
That logic doesn't work because det(A+A') is not equal to det(A)+det(A'). You need to think of something else ThankYou. Might it be that A+A' has two identical rows? How can you use that? You don't need the premise that A is invertible.

That logic doesn't work because det(A+A') is not equal to det(A)+det(A'). You need to think of something else ThankYou. Might it be that A+A' has two identical rows? How can you use that? You don't need the premise that A is invertible.

Ha...
I've just got the Homework result back...
88
I got -6 for this question..
I know about the two identical lines but it did not used the fact that A is invertible...

Actually they just put the invertible fact to confuse because the teacher solution was the same as Dick without using the invertible Fact

Thanks anyway.