Pappu's Theorem

If A1, B1, and C1 are three points on a line, and A2 , B2 and C2 are three points on a second line.If A1B2 meets A2B1 at X, and A1C2 meets A2C1 at Y, and B1C2 meets B2C1 at Z, then X, Y, and Z are collinear (on a straight line).

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