Why is Ax in col(A) if (A^T)Ax=0

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SUMMARY

The discussion clarifies that if \( (A^T)Ax = 0 \), then \( Ax \) is indeed in the column space of matrix \( A \). The participants confirm that \( Ax \) is always in col(A) regardless of the specific matrices \( A \) and vector \( x \). Additionally, it is noted that \( Ax \) is orthogonal to col(A) when \( x = 0 \), which can lead to confusion. The key takeaway is the consistent relationship between \( Ax \) and col(A).

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  • Understanding of linear algebra concepts, particularly matrix multiplication.
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horefaen
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Can someone explain why Ax is in col(A) if (A^T)Ax=0, A^T is the transpose.

Note: Ax is also orthogonal to col(A),(so x=0) so don't let that confuse you.
 
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Isn't Ax always in col(A), no matter what A and x are?
 
Yes it is, I know see it, I missed it, thank for your answer.
 

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