б) $$ \frac{y^6 - y^8}{y^4 - y^2} = \frac{y^6(1 - y^2)}{y^2(y^2 - 1)} = \frac{-y^6(y^2 - 1)}{y^2(y^2 - 1)} = -y^4 $$
Ответ: $$-y^4$$