What's the remainder when $x^{7} + x^{27} + x^{47} +x^{67} + x^{87}$ is divided by $x ^ 3 - x$ What's the remainder when $x^{7} + x^{27} + x^{47} +x^{67} + x^{87}$ is divided by $x ^ 3 - x$ in terms of $x$?I tried factoring $x$ from both polynomials but I don't know what to do next since there'd be a $1$ in the second polynomial.
Any help would be appreciated!

Modulo $x^3-x$ we have $x^3=x$ so $x^{2n+1}=x$ for any integer $n\ge 0$ (a trivial induction exercise). Hence your sum leaves remainder $5x$.
