Let $A$ and $B$ be $2\times 2$ matrices such that $A^2 - B^2$ is invertible. Is $A-B$ necessarily invertible?
This doesn't seem like it should be difficult but I just can't come up with a solution.
Let $A$ and $B$ be $2\times 2$ matrices such that $A^2 - B^2$ is invertible. Is $A-B$ necessarily invertible?
This doesn't seem like it should be difficult but I just can't come up with a solution.
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The answer is no. For instance, consider $$ A = \pmatrix{0&1\\1&0}, \quad B = \pmatrix{0&1\\0&0}. $$