A triangle or threesided figure is the prime or most simple figure of all rectilineals. For amongst rectilineall figures there is none of two sides: For two right lines cannot inclose a figure. What is meant by a prime figure, was taught at the [11. e. iiij].
And
8. If an infinite right line doe cut the angle of a triangle, it doth also cut the base of the same: Vitell. 29. t j.
9. Any two sides of a triangle are greater than the other.
Thus much of the difinition of a triangle; the reason or
rate in the sides and angles of a triangle doth follow. The reason of the sides is first.
Let the triangle be aei; I say, the side ai, is shorter, than the two sides ae, and ei, because by the [6. e ij], a right line is betweene the same bounds the shortest.
Therefore
