Ответ:\(\frac{4x-y+x+y}{x^2-y^2}=\frac{5x}{x^2-y^2}\).\(\frac{y^2-y(y-9)}{(y-9)(y+9)}=\frac{9y}{y^2-81}\).\(\frac{10a-(5a-3)}{(5a-3)(5a+3)}=\frac1{5a-3}\).\(\frac{n(n-7)-n^2}{(n-7)^2}=-\frac7{(n-7)^2}\).