Find the remainder of f(x) divided by x^2 - 1 when f(x) = x^10 - 8x^8+7x^4+ 8x^3-12x^2 -15x - 5.
We have $x^{10}-8x^8+7x^4+8x^3-12x^2-15x-5 = (x^2-1)(x^8-7x^6-7x^4+8x-12)-7x-17$. So the remainder is $-7x-17$.
