Решить систему уравнений способом постановки (а.б)

1) $\left \{ {{ x^{2} + xy- y^{2} =11} \atop {x-2y=1}} \right. \\ \\ x=1+2y \\ (1+2y)^{2} +y+2y^{2}- y^{2}=11 \\ 1+4y+ 4y^{2} +y+ 2y^{2}- y^{2} =11 \\ 5y^{2}+5y-10=0 \\ y^{2} +y-2=0 \\ \sqrt{D} = \sqrt{1+8} = \sqrt{9} =3 \\ x_{1} = \frac{-1-3}{2}=-2 \\ x_{2} = \frac{-1+3}{2}=1 \\ y= \frac{x-1}{2} \\ y_{1}= \frac{-2-1}{2}=-1,5 \\ y_{2}= \frac{1-1}{2}=0$
2) $\left \{ {{xy+ y^{2}+x-3y=15 } \atop {x+y=5}} \right. \\ \\ x=5-y \\ 5y- y^{2} + y^{2} +5y-y-3y=15 \\ 6y=15 \\ y=2,5 \\ x=5-2,5=2,5$