由题意知a^2-b^2=1,将点(-1,√2/2)代入椭圆方程得1/a^2+1/2b^2=1解得,椭圆方程为x^2/2+y^2=1设点A(x1,y1),B(x2,y2),则QA=(x1-5/4,y1),QB=(x2-5/4,y2)(1)若直线l斜率为零,点A,B分别为(-√2,0)(√2,0)此时向量之积为-7/16(2)若直线斜率不为0,则设直线方程为x=ky+1与椭圆方程联立,得,(k^2+2)y^2+2ky-1=0则有y1+y2=-2k/(k^2+2)y1·y2=-1/(k^2+2)则x1+x2=k(y1+y2)+2x1·x2=k^2y1·y2+k(y1+y2)+1则有,QA·QB=(k^2+1)y1·y2-k/4(y1+y2)+1/16=-(k^2+1)/(k^2+2)+k/4·2k/(k^2+2)+1/16=-7/16综上所述,两向量之积为定值,-7/16