A Course of Plane Geometry for Advanced Students Part 1

  title={A Course of Plane Geometry for Advanced Students Part 1},
  author={Marian van der Meij},
THIS is a really capital book for students of what may be called scholarship standard. It contains, among other things, sections on similarity, transversals, vector geometry, inversion, and coaxal circles. As examples of the author's choice of elegant methods, and his clearness of exposition, may be taken the proof (due to Mr. Hillyer) that the centres of the diagonals of a complete quadrilateral are.collinear (p. 118), and the proof of Feuerbach's theorem by inversion (p. 149). In the latter… 
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Watt linkages and quadrilaterals
We define a Watt quadrilateral to be a quadrilateral with a pair of opposite sides of equal length. See Figure 1. 2. Linkages The Watt linkage (Figure 2) has equal-length cranks AD and BC, A and B