关于直线划分平面有一个容易记忆,应用方便的重要结论。即,直线l:f(x,y)≡Ax+By+C=0(简记为f(x,y)=0)把平面上不在l上的点划分成两个区域,点P_1(x_1,y_1)和P_2(x_2,y_2)在同一个区域(或在不同区域)的充要条件是函数值f(x_1,y_1)和f(x_2,y_2)同号(或异号)(见文[2])。对于圆锥曲线Γ:F(x,y)≡Ax~2+2Bxy+Cy~2+2Dx+2Ey+F=0(简记为F(x,y)=0),如果我们约定,圆 There are important conclusions about the straight line dividing plane which is easy to remember and convenient to use. That is, the line l:f(x,y)≡Ax+By+C=0 (abbreviated as f(x,y)=0) divides the point not on l in the plane into two regions, the point P_1 (x_1) The necessary and sufficient condition for y_1) and P_2(x_2, y_2) in the same region (or in different regions) is that the function values ​​f(x_1, y_1) and f(x_2, y_2) have the same number (or different sign) (see text) [2]). For conic curves Γ: F(x,y)≡Ax~2+2Bxy+Cy~2+2Dx+2Ey+F=0 (abbreviated as F(x,y)=0), if we agree, circle