The 25-Pin Lattice Geoboard
Fig. 10b
Putting another band on the board with the same nail as its mid point, he has two lines clearly bisecting each other.
Fig. 10c
By placing another band on the four end nails of the two lines, he constructs a parallelogram (or a rectangle or a square according to what was done, but nothing else in the 9-pin Geoboard, also a rhombus on the 25-pin one).
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