в) (a/b - b/a) : (a + b) / 3ab

1. $\left( \frac{a}{b} - \frac{b}{a} \right) : \frac{a + b}{3ab} = \frac{a^2 - b^2}{ab} \cdot \frac{3ab}{a + b} = \frac{(a - b)(a + b)}{ab} \cdot \frac{3ab}{a + b} = 3(a - b) = 3a - 3b$ 2. $\left( 1 - \frac{2c}{d} + \frac{c^2}{d^2} \right) \cdot \frac{d}{c - d} = \left( \frac{d^2 - 2cd + c^2}{d^2} \right) \cdot \frac{d}{c - d} = \frac{(d - c)^2}{d^2} \cdot \frac{d}{c - d} = \frac{(c - d)^2}{d^2} \cdot \frac{d}{c - d} = \frac{c - d}{d}$ 3. $\left( 4p - \frac{q^2}{p} \right) : \left( 1 - \frac{2p}{q} \right) = \frac{4p^2 - q^2}{p} : \frac{q - 2p}{q} = \frac{(2p - q)(2p + q)}{p} \cdot \frac{q}{-(2p - q)} = -\frac{q(2p + q)}{p} = -\frac{2pq + q^2}{p}$ 4. $\left( \frac{r}{s} - 2 \right) : \frac{4s - 2r}{rs^2} = \frac{r - 2s}{s} \cdot \frac{rs^2}{2(2s - r)} = \frac{r - 2s}{s} \cdot \frac{rs^2}{-2(r - 2s)} = -\frac{rs}{2}$ 5. $\frac{z - 3}{z + 3} \cdot \left( z + \frac{z^2}{3 - z} \right) = \frac{z - 3}{z + 3} \cdot \left( \frac{3z - z^2 + z^2}{3 - z} \right) = \frac{z - 3}{z + 3} \cdot \frac{3z}{-(z - 3)} = -\frac{3z}{z + 3}$ 6. $\left( \frac{q}{q - 5} - 2q \right) : \frac{11 - 2q}{q - 5} = \left( \frac{q - 2q(q - 5)}{q - 5} \right) : \frac{11 - 2q}{q - 5} = \left( \frac{q - 2q^2 + 10q}{q - 5} \right) \cdot \frac{q - 5}{11 - 2q} = \frac{11q - 2q^2}{q - 5} \cdot \frac{q - 5}{11 - 2q} = \frac{q(11 - 2q)}{11 - 2q} = q$