(y - 4y) : (3/4х - 2 3/4)

при у = -1/3; х = 1/2

((-1/3) - 4(-1/3)) : (3/4*1/2 - 2 3/4) = (-1/3 + 4/3) : (3/8 - 11/4) = 1 : (-19/8) = -8/19

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Если во второй скобке у второй дроби присутствует х:

(y - 4y) : (3/4х - 2 3/4х)

при у = -1/3; х = 1/2

((-1/3) - 4(-1/3)) : (3/4*1/2 - 2 3/4*1/2) = (-1/3 + 4/3) : (3/8 - 11/8) = 1 : (-1) = -1