10) (x²−y²)/a − 2x²/a =

\(\frac{x^2-y^2}{a}-\frac{2x^2}{a}=\frac{x^2-y^2-2x^2}{a}=\frac{-x^2-y^2}{a}\).

Ответ: \(-\frac{x^2+y^2}{a}\)