Is there a $3 \times 3$ matrix $A$ that satisfies $A = A^3$ and $\det(A) = 3$? Justify your answer.
Past exam paper question I can't get.
Is there a $3 \times 3$ matrix $A$ that satisfies $A = A^3$ and $\det(A) = 3$? Justify your answer.
Past exam paper question I can't get.
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Since $\det(A)=3\ne0$, thus $A$ is invertible. Then from $A=A^3$ we have $$A^{-1}A=A^{-1}A^3\Rightarrow I=A^2$$ which implies $$\det I=\det A^2=(\det A)^2$$ i.e. $$1=(\det A)^2$$ or $\det A= \pm 1$, which contradicts our assumption that $\det A=3$.