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平面中一条直线把整个平面分成两个半平面，我们称它们为直线的两个“侧”．取定一直角坐标系．设直线ｌ的方程为Ａｘ＋Ｂｙ＋Ｃ＝０①（Ａ，Ｂ不同时为零）．当一点Ｐ（ｘ０，ｙ０）不在ｌ上时，把它代入①的左端必不为零．容易证明，在ｌ同（异）侧的点的坐标代入①左端...
A straight line in the plane divides the entire plane into two half planes. We call them two “sides” of the line. Set the straight angle coordinate system. Let the equation of the line l be Ax+By+C=01 (A, B are not zero at the same time). When the point P(x0, y0) is not on l, the left end of it is not zero. It is easy to prove that the coordinates of the points on the same (iso) side are substituted into the left side of 1...