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\( \dfrac{x^{2}+5y}{x-3y} - \dfrac{7y+x^{2}}{x-3y} = \dfrac{x^{2}+5y-(7y+x^{2})}{x-3y} = \dfrac{x^{2}+5y-7y-x^{2}}{x-3y} = \dfrac{-2y}{x-3y} = \dfrac{2y}{3y-x} \) .

а) \(\dfrac{4a^{2}-1}{a-1} + \dfrac{1-2a^{2}}{a-1} =\) [ ].

б) \(\dfrac{3x-4y}{x+y} - \dfrac{2x-y}{x+y} =\) [ ].

в) \(\dfrac{a^{2}-2ab}{a-2b} + \dfrac{ab-a^{2}}{a-2b} =\) [ ].

г) \(\dfrac{2c-d}{c+2d} - \dfrac{c-d}{c+2d} =\) [ ].