已知圆O,：x^2+y^2=4和直线：x+y+√b=0相交于A,B两点,则OA向量×OB向量=?
问题描述：
已知圆O,：x^2+y^2=4和直线：x+y+√b=0相交于A,B两点,则OA向量×OB向量=?
答
A(x1,y1) B(x2,y2) OA向量×OB向量=x1x2+y1y2 y1y2=x1x2+√b(x1+x2)+b
x^2+y^2=4和直线：x+y+√b=0 x^2+√bx+b/2-2=0 x1x2=b/2-2 x1+x2=-√b
OA向量×OB向量=x1x2+y1y2=2x1x2+√b(x1+x2)+b=b-4