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Let $A: \mathbb{R}^{n} \rightarrow \mathbb{R}^{k}$ be a real matrix, not necessarily square.

a) If two rows of $A$ are the same, show that $A$ is not onto by finding a vector $y=$ $\left(y_{1}, \ldots, y_{k}\right)$ that is not in the image of $A$. [HINT: This is a mental computation if you write out the equations $A x=y$ explicitly.]
b) What if $A: \mathbb{C}^{n} \rightarrow \mathbb{C}^{k}$ is a complex matrix?
c) More generally, if the rows of $A$ are linearly dependent, show that it is not onto.
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