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How do I factorise $r^4+r^2+1$ ? $(r^2+r+1)(r^2-r+1)$ gives $r^4+r^2+1$ But how to split it into these factors? I generally find roots and then write the factors, but $r^4+r^2+1$ seems to have no real root. Thanks!

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One may start with $$ r^4+r^2+1=(r^4+2r^2+1)-r^2=(r^2+1)^2-r^2. $$

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$$x^4+x^2+1=\frac{x^6-1}{x^2-1}=\frac{(x^3-1)(x^3+1)}{(x-1)(x+1)} =(x^2+x+1)(x^2-x+1).$$

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