3. Выполните действия: a) $$\frac{3x}{4(y-5)} - \frac{6x}{7(y-5)}$$ б) $$\frac{6b}{3-2a} + 3 - \frac{5a+8}{2a-3}$$

Решение:

а)

\(\frac{3x}{4(y-5)} - \frac{6x}{7(y-5)} = \frac{3x \cdot 7 - 6x \cdot 4}{28(y-5)} = \frac{21x - 24x}{28(y-5)} = \frac{-3x}{28(y-5)}\)

б)

\(\frac{6b}{3-2a} + 3 - \frac{5a+8}{2a-3} = \frac{-6b}{2a-3} + 3 - \frac{5a+8}{2a-3} = \frac{-6b + 3(2a-3) - (5a+8)}{2a-3} = \frac{-6b + 6a - 9 - 5a - 8}{2a-3} = \frac{a - 6b - 17}{2a-3}\)

Ответ: а) $$\frac{-3x}{28(y-5)}$$; б) $$\frac{a - 6b - 17}{2a-3}$$