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Ad Quadratum Construction and Study of the Regular Polyhedra

Ad Quadratum Construction and Study of the Regular Polyhedra

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31<br />

Now, consider triangles AA HO <strong>and</strong> AA BJ<br />

, where A A is<br />

<strong>the</strong> point view <strong>of</strong> line AA’,<br />

simplified to A in <strong>the</strong> following:<br />

AO HO<br />

<br />

AB BJ<br />

or, replacing by <strong>the</strong> values indicated on <strong>the</strong> figure<br />

a<br />

<br />

a <br />

2<br />

r<br />

a<br />

<br />

<br />

<br />

r<br />

a<br />

<br />

But in BJO,<br />

I ˆ i<br />

Rcos<br />

2<br />

<br />

<br />

a<br />

<br />

r<br />

R cos ˆ<br />

I i<br />

2<br />

or: r I ˆ i<br />

cos<br />

R 2<br />

Now referring to <strong>the</strong> initial adquadratum construction diagram (fig. 13), <strong>and</strong> considering<br />

triangle D we can write:<br />

cos ˆ D i O 2 1<br />

.<br />

OD 3<br />

And making use <strong>of</strong> <strong>the</strong> identity cos A 1<br />

1cos A,<br />

2 2<br />

But, from <strong>the</strong> well-known identity 1 <br />

D ˆ i 1<br />

2 1<br />

we have: cos 1 <br />

2 2 3 <br />

<br />

1 2<br />

2 1<br />

<br />

2 3 3<br />

,

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