Ответ: [tex] \frac{3x}{4x — 4} + \frac{5x}{7 — 7x} = \frac{3x}{4(x — 1)} + \frac{5x}{7(1 — x)} = \frac{3x}{4(x — 1)} — \frac{5x}{7(x — 1)} = \frac{21x + 20x}{28(x — 1)} = \frac{41x}{28x — 28)} [/tex]