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Решите задачу:

$\dfrac{2a - 6 b}{18b - 6a} = \dfrac{2 (a - 3 b)}{6(3b - a)} = \dfrac{-(3b -a)}{3(3b - a)} = -\dfrac{1}{3}$

$\dfrac{15m - 6 n}{2n - 5m} = \dfrac{3 (5m -2n)}{-(5m - 2n)} = -3$

$\dfrac{4x^2 - 5xy}{10y - 8x} = \dfrac{x(4x-5y)}{-2(4x-5y)} = -\dfrac{x}{2}$

$\dfrac{12xy - 9 y^2}{3y^2 x -4yx^2} = \dfrac{-3y (3y - 4x)}{xy(3y - 4x)} = -\dfrac{3}{x}$

$\dfrac{25a^2 - 9}{5a+3} = \dfrac{(5a-3) (5a+3)}{5a+3} = 5a-3$

$\dfrac{49x^2 - 64y^2}{7x - 8y} = \dfrac{(7x+8y)(7x-8y)}{7x-8y} = 7x+8y$