The 25-Pin Lattice Geoboard
Fig. 20a
Fig. 20b
Considering one of the triangles only, we can insert three rubber bands either as altitudes or medians. In both cases they appear to be concurrent.
Fig. 21a
Fig. 21b
We have first to establish that the lines we called ‘altitudes’ are truly perpendicular. This is proved by showing that, on reproducing on a similar board one line representing one of the altitudes and another representing the corresponding side of the triangle, and rotating the board a quarter of a revolution round the centre point, one of the lines exactly takes the place of the
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