Решение:

a)

$$\left(\frac{a}{m} + \frac{a^2}{m^3}\right) : \left(\frac{m^2}{a^2} + \frac{m}{a}\right) = \frac{am^2 + a^2}{m^3} : \frac{m^2 + ma}{a^2} = \frac{a(m^2 + a)}{m^3} \cdot \frac{a^2}{m(m + a)} = \frac{a^3(m^2 + a)}{m^4(m + a)}$$

б)

$$\frac{x-2}{x-3} \cdot \left(x + \frac{x}{2-x}\right) = \frac{x-2}{x-3} \cdot \left(\frac{x(2-x) + x}{2-x}\right) = \frac{x-2}{x-3} \cdot \frac{2x - x^2 + x}{2-x} = \frac{x-2}{x-3} \cdot \frac{3x - x^2}{2-x} = \frac{x-2}{x-3} \cdot \frac{x(3 - x)}{2-x} =$$ $$\frac{(x-2) \cdot x \cdot (3 - x)}{(x-3) \cdot (2-x)} = \frac{-(2-x) \cdot x \cdot (3-x)}{(x-3) \cdot (2-x)} = \frac{-x(3-x)}{x-3} = \frac{x(x-3)}{x-3} = x$$

2

$$\frac{3a + 6b}{\frac{2a^2 - 8b^2}{a+b}} = \frac{3(a + 2b)}{\frac{2(a^2 - 4b^2)}{a+b}} = \frac{3(a + 2b)}{\frac{2(a - 2b)(a + 2b)}{a+b}} = \frac{3(a + 2b) \cdot (a+b)}{2(a - 2b)(a + 2b)} = \frac{3(a+b)}{2(a - 2b)}$$ Подставим значения a = 26 и b = -12: $$\frac{3(26 - 12)}{2(26 - 2(-12))} = \frac{3 \cdot 14}{2(26 + 24)} = \frac{3 \cdot 14}{2 \cdot 50} = \frac{3 \cdot 7}{50} = \frac{21}{50} = 0.42$$

Ответ: 0.42