{1+x2=a214+y2=a22x+y=1\left\{ \begin{array}{l} 1+x^2=a^2 \\ \frac{1}{4}+y^2=\frac{a^2}{2} \\x+y=1 \end{array} \right. ⎩⎨⎧1+x2=a241+y2=2a2x+y=1 求 a,x,ya,x,ya,x,y
