过Q（1,1）做双曲线(x^2)/4-(y^2)/2 = 的弦MN,使Q为MN的中点 ,求MN方程和弦长

用点差法的过程是这样:记M(x1,y1)N(x2,y2) 所在直线y-1=k(x-1)(x1+x2)/2=1(y1+y2)/2=1(x1^2)/4-(y1^2)/2=1(x2^2)/4-(y2^2)/2=1相减得(x1+x2)(x1-x2)/4-(y1+y2)(y1-y2)/2=0k=(y1-y2)/(x1-x2)=2(x1+x2)/4(y1+y2)=1/2∴...