# What is the minimal polynomial AB?

Let $A\in M_{n}(R)$ with the minimal polynomial $x^{2}-1$ and $B\in M_{n}(R)$ with the minimal polynomial $x^{2}+1$. What is the minimal polynomial $AB$ if $AB=BA$?

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Fix your accept rate. –  B. S. Dec 12 '12 at 17:48
I find the answer. The answer is $x^{2}+1$.