[tex]dla \ \ x = \frac{1}{3} \ \ i \ \ y = 9\\\\\\a) \ 2x^{2}-xy^{2}-5x^{2}+2xy^{2} = xy^{2}-3x^{2} = \frac{1}{3}\cdot9^{2}-3\cdot(\frac{1}{3})^{2} =\frac{1}{3}\cdot81-3\cdot\frac{1}{9} =27-\frac{1}{3} = 26\frac{2}{3}[/tex]
[tex]b) \ -\frac{1}{2}x^{3}y -\frac{2}{3}xy+\frac{1}{2}x^{3}y -\frac{1}{3}xy = -\frac{3}{3}xy = -1\cdotxy = -xy = -(\frac{1}{3}\cdot9) = -\frac{9}{3} = -3[/tex]
