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If $\mathbb{R}^n=\operatorname{span}\{X_1,X_2,...,X_k\}$ and $A$ is an $m\times n$ matrix, does $AX_i$ not equal $0$ for some $i$?

I think the answer might be no. But when I tried to prove it, I notice the way I did is not so persuasive. Can anybody help?

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    Do you mean 0 matrix? This question would be meaningless if$A$is 0 matrix.2012-01-27

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Note that if $AX_i=0$ for all $i$ then $A(a_1X_1+...+a_kX_k)=0$. Thus, as $span\{X_1,...,X_k\}=\mathbb R^n$, it follows that $AX=0$ for all $X\in \mathbb R^n$. Therefore $AX_i=0$ for all $i$ if and only if $A$ is the zero-matrix.

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    Talked to the prof today that he made some revision and stated$A$should be nonzero matrix. Thank you all.2012-01-27