1) (2x^4/(y^4-x^4) : (x² /( x²+y) =2·x²·(x²+y) / (y^4-x^4)
2 ) ( ( y+ x² ) / (y² - x²) + 2·x²·(x²+y)/(y^4-x^4) =
( y + x²) / (y² - x²) + 2·x²·(y + x²) /( y²-x²)·( y²+x²) =
((y + x²)·(y²+x²) + 2·x²·(y + x²)) /( (y²-x²)·(y²+x²)) =
((y + x² )·(y² + x² + 2 x²))/ ( (y² - x² )· (y²+ x²)) = (y+x²)·(y²+3x²) /y^4-x^4