Вычисления и преобразования

$$\frac{0,6 \cdot 0,09}{\frac{1}{25}} = 0,054 \cdot 25 = 1,35$$

$$\left(\dfrac{3}{4} + 2\dfrac{3}{8}\right) \cdot 25,6 = \left(\dfrac{3}{4} + \dfrac{19}{8}\right) \cdot 25,6 = \left(\dfrac{6}{8} + \dfrac{19}{8}\right) \cdot 25,6 = \dfrac{25}{8} \cdot 25,6 = \dfrac{25 \cdot 25,6}{8} = 25 \cdot 3,2 = 80$$

$$a(36a^2 - 25)\left(\dfrac{1}{6a+5} - \dfrac{1}{6a-5}\right) = a(36a^2 - 25) \cdot \dfrac{(6a-5) - (6a+5)}{(6a+5)(6a-5)} =$$ $$= a(36a^2 - 25) \cdot \dfrac{-10}{36a^2 - 25} = a \cdot (-10) = -10a$$ При $a = 36,7$: $$-10 \cdot 36,7 = -367$$

$$(9b^2 - 49)\left(\dfrac{1}{3b-7} - \dfrac{1}{3b+7}\right) + b - 13 = (9b^2 - 49) \cdot \dfrac{(3b+7) - (3b-7)}{(3b-7)(3b+7)} + b - 13 =$$ $$(9b^2 - 49) \cdot \dfrac{14}{9b^2 - 49} + b - 13 = 14 + b - 13 = b + 1$$ При $b = 345$: $$345 + 1 = 346$$

$$\left(2\dfrac{4}{7} - 1,2\right) \cdot 5\dfrac{5}{6} = \left(\dfrac{18}{7} - \dfrac{6}{5}\right) \cdot \dfrac{35}{6} = \left(\dfrac{90}{35} - \dfrac{42}{35}\right) \cdot \dfrac{35}{6} = \dfrac{48}{35} \cdot \dfrac{35}{6} = \dfrac{48}{6} = 8$$