1)

[tex] \frac{a(x - 2y)}{b(2y - x)} = \frac{ - a(2y - x)}{b(2y - x)} = - \frac{a}{b} [/tex]

2)

[tex] \frac{3a - 36}{12b - ab} = \frac{3(a - 12)}{ - b(a - 12)} = - \frac{3}{b} [/tex]

3)

[tex] \frac{25 - {a}^{2} }{3a - 15} = \frac{ - (a - 5)(a + 5)}{3(a - 5)} = - \frac{a + 5}{3} [/tex]

4)

[tex] \frac{8 {b}^{2} - 8 {a}^{2} }{ {a}^{2} - 2ab + {b}^{2} } = \frac{ - 8(a + b)(a - b)}{(a - b) {}^{2} } = - \frac{8a + 8b}{a - b} [/tex]

5)

[tex] \frac{5x(x - y)}{ {x}^{3}(y - x) } = \frac{5(x - y)}{ - {x}^{2}(x - y) } = - \frac{5}{ {x}^{2} } [/tex]

6)

[tex] \frac{7b - 14 {b}^{2} }{42 {b}^{2} - 21b} = \frac{ - 7b(2b - 1)}{21b(2b - 1)} = - \frac{b}{3} [/tex]

7)

[tex] \frac{3 - 3x}{ {x}^{2} -2 x + 1 } = \frac{ - 3(x - 1)}{(x - 1) {}^{2} } = - \frac{3}{x - 1} [/tex]

8)

[tex] \frac{(b - 2) {}^{3} }{(2 - b) {}^{2} } = \frac{ - (2 - b) {}^{3} }{(2 - b) {}^{2} } = - (2 - b) = b - 2[/tex]