9) (x²−y²)/a + 2x²/a =

\(\frac{x^2-y^2}{a}+\frac{2x^2}{a}=\frac{x^2-y^2+2x^2}{a}=\frac{3x^2-y^2}{a}\).

Ответ: \(\frac{3x^2-y^2}{a}\)