506. 1) \((3\frac{2}{3}k-1\frac{2}{5}l)^2\); 2) \((0,5b-0,4c)^2\).

Преобразуем смешанные числа: \(3\frac{2}{3}=\frac{11}{3}\), \(1\frac{2}{5}=\frac{7}{5}\).

1. \((\frac{11}{3}k-\frac{7}{5}l)^2=\frac{121}{9}k^2-2\cdot\frac{11}{3}k\cdot\frac{7}{5}l+\frac{49}{25}l^2=\frac{121}{9}k^2-\frac{154}{15}kl+\frac{49}{25}l^2\).
2. \((0.5b-0.4c)^2=(0.5b)^2-2\cdot0.5b\cdot0.4c+(0.4c)^2=0.25b^2-0.4bc+0.16c^2\).

Ответ: 1) \(\frac{121}{9}k^2-\frac{154}{15}kl+\frac{49}{25}l^2\); 2) \(0.25b^2-0.4bc+0.16c^2\).