Hayes solves the problem of determining whether three points in a plane are collinear.

Hayes解决了如何确定一个平面上的三个点是否在一条直线上的问题。

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With some examples in plane geometry, the author indroduces how to use Desargues theorem to simplify the proofs of problems of collinear points and concurrent lines.

利用代沙格定理及其逆定理 ，对平面几何的几个共线点和共点线的问题给出简捷的证法。

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