T H E E L E M E N T S |
Book IV Proposition 15 | |
The triangle EGD is equilateral; and therefore its three angles EGD, GDE, DEG are equal to one another, inasmush as, in isosceles triangles, the angles at the base are equal to one another. [I.5] And the three angles of the triangle are equal to two right angles; [I.32] therefore the angle EGD is one-third of two right angles. Similarly, the angle DGC can also be proved to be one-third of two right angles. |
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