[tex]b)\\\\2x^2-x(x-y)+y(x-3)=2x^2- x^2+xy +xy-3y=x^2+2xy-3y\\\\x=\frac{1}{2},\ \ \ y=2,5=\frac{25}{10}=\frac{5}{2}\\\\x^2+2xy-3y= (\frac{1}{2}) ^2+\not{2}^1* \frac{1}{\not{2}^1}*\frac{5}{2}-3 *\frac{5}{2}=\frac{1}{4} +\frac{5}{2}-\frac{15}{2}=\\\\=\frac{1}{4}+\frac{10}{4}-\frac{30}{4}=-\frac{19}{4}=-4\frac{3}{4}[/tex]
