“已知曲线P上的任意一点M(x,y),适合几何条件p(M),求曲线P的方程”这类问题在平面解析几何里占有重要地位。经验告诉我们,解这类问题必须注意两点,否则易出差错。〔注意一〕.将曲线P(点集P)改写为集合 “Any point on the known curve P M (x, y), suitable for the geometric condition p (M), the equation for the curve P” This type of problem occupies an important position in the plane analytical geometry. Experience tells us that we must pay attention to two points in solving this kind of problem, otherwise it is easy to go wrong. 〔Note 1〕. Rewrite curve P (point set P) as a set