487 3) 3(x+y) x2 + y2 4y² (x² + y²) x2 − y 2

3) $$ \frac{3(x+y)}{4y^2(x^2+y^2)} : \frac{x^2+y^2}{x^2-y^2} = \frac{3(x+y)}{4y^2(x^2+y^2)} \cdot \frac{x^2-y^2}{x^2+y^2} = \frac{3(x+y)(x-y)(x+y)}{4y^2(x^2+y^2)(x^2+y^2)} = \frac{3(x^2-y^2)}{4y^2(x^2+y^2)^2} $$

Ответ: $$ \frac{3(x^2-y^2)}{4y^2(x^2+y^2)^2} $$