\(\dfrac{x^{10}-x^8+x^6-x^4+x^2-1}{x^4-1}\)
\(=\dfrac{\left(x^{10}-x^8\right)+\left(x^6-x^4\right)+\left(x^2-1\right)}{x^4-1}\)
\(=\dfrac{x^8\left(x^2-1\right)+x^4\left(x^2-1\right)+1\left(x^2-1\right)}{x^4-1}\)
\(=\dfrac{\left(x^8+x^4+1\right)\left(x^2-1\right)}{x^4-1}\)
\(=\dfrac{\left(x^8+x^4+1\right)\left(x^2-1\right)}{\left(x^2+1\right)\left(x^2-1\right)}\)
\(=\dfrac{x^8+x^4+1}{x^2+1}\)