505. 1) (\frac{x}{2}-\frac{y}{3})²; 2) (\frac{a}{4}+\frac{b}{3})²; 3) (2\frac{1}{3}m+1\frac{1}{2}n)²;

1) $$(\frac{x}{2} - \frac{y}{3})^2 = \frac{x^2}{4} - \frac{xy}{3} + \frac{y^2}{9}$$ 2) $$(\frac{a}{4} + \frac{b}{3})^2 = \frac{a^2}{16} + \frac{ab}{6} + \frac{b^2}{9}$$ 3) $$(2\frac{1}{3}m + 1\frac{1}{2}n)^2 = (\frac{7}{3}m + \frac{3}{2}n)^2 = \frac{49}{9}m^2 + \frac{14}{2}mn + \frac{9}{4}n^2 = \frac{49}{9}m^2 + 7mn + \frac{9}{4}n^2$$