29.²-2xy + y².

29. $$\frac{9}{16}x^2 - 2xy + \frac{16}{9}y^2 = (\frac{3}{4}x)^2 - 2(\frac{3}{4}x)(\frac{4}{3}y) + (\frac{4}{3}y)^2 = (\frac{3}{4}x - \frac{4}{3}y)^2$$

Ответ: $$(\frac{3}{4}x - \frac{4}{3}y)^2$$