I have an assignment problem:
Which statement(s) about an $n \times n$ matrix $A$ is/are always true?
If the rank of $A$ is $n$, then $A$ is diagonalizable.
If $A$ has $n$ distinct eigenvalues, then $A$ is diagonalizable.
If one or more of the eigenvalues of $A$ is $0$, then $A$ cannot be diagonalized.
I know that $\#2$ is true, because if it has $n$ distinct eigenvalues, then it has $n$ linearly independent eigenvectors, then it is diagonalizable.
I know that $\#3$ is false, for example the matrix of all zeroes is diagonalizable (since it's already diagonal) and has zero eigenvalues, so $\#3$ is clearly false.
I am not sure about $\#1$. I know that rank $n$ means that the columns are all linearly independent. I think it means that it is diagonalizable but I am not certain.
Thanks for help.