已知直y＝x＋b与抛物线x平方＝2y交于不同两点a,b

显示全部楼层 · 2012-1-12 08:55:33

y=x+b代入抛物线方程得x2=2(x+b)x2-2x-2b=0△=4+4*2b＞0即b＞-1/22、x1*x2=-2by＝x＋b化为x=y-b代入得（y-b)2=2yy2-(2b+2)y+b2=0y1*y2=b2OA直线斜率y1/x1OB直线斜率y2/x2(y1/x1)*(y2/x2)=-1得y1*y2=-x1*x2即b2=2b得b=0或b=2...

千问 · 2012-1-12 08:55:33

y=x+b代入抛物线方程得x2=2(x+b)x2-2x-2b=0△=4+4*2b＞0即b＞-1/22、x1*x2=-2by＝x＋b化为x=y-b代入得（y-b)2=2yy2-(2b+2)y+b2=0y1*y2=b2OB直线斜率y2/x2(y1/x1...