50 БАЛЛОВ СРОЧНО ЗА ГОЛовой :n^2-2n/xy+3y+

$\frac{n^2 - 4}{x^2 - 9} : \frac{n^2 - 2n}{xy+3y} + \frac{2-y}{x - 3} = \\ \\ = \frac{n^2-2^2}{x^2-3^2} : \frac{n(n-2)}{y(x+3)} +\frac{2-y}{x - 3} = \\ \\ = \frac{(n-2)(n+2)}{(x-3)(x+3)} * \frac{y(x+3)}{n(n-2)} + \frac{2-y}{x - 3} = \\ \\ = \frac{1*(n+2)*y*1}{(x-3)*1*n*1} +\frac{2-y}{x - 3} = \\ \\ = \frac{y(n+2)}{n(x-3)} +\frac{2-y}{x - 3} = \frac{y(n+2)+n(2-y)}{n(x-3)} = \\ \\ = \frac{yn+2y +2n -yn}{n(x-3)} = \frac{2y+2n}{n(x-3)} = \\ \\ = \frac{2(y+n)}{n(x-3)}$

$n= 3;x=-4 ; y = -5 \\ \\ \frac{2(-5+3)}{3(-4-3)} = \frac{2*(-2)}{3*(-7)} = \frac{-4}{-21} = \frac{4}{21}$

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