Schol.
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If to any right line GH, and in it a point A, two right lines being drawn EA, AF, and not taken on the fame hde,make the vertical (or oppoſite) angles D and B equal, thoſe right lines EA, AF, do meet directly and make one ſtrait line.
For two right angles are a equal to the angle * T * D-^AtfrB A. b therefore, EA, AF, are in a b x 4- *• ſtrait line. Which was to be demonſtrated.
Schol.
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If four right lines EA, EB, EC, ED, proceeding from one point E, make the angles vertically oppoſite equal the one to the other, each two lines, AE, EB, and CE, ED, are placed in one ſtrait line.
For becauſe the angle AEC + AED + CEB + DEB a = to 4 right angles, therefore the anglea 4.c.13.1.
b hyp. and
2.ax.
c 14.1.AEC + AED b = CEB + DEB = to two right angles, c therefore CED and AEB are, ſtrait lines. Which was to be demonſtrated.
PROP. XVI.
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One ſide BC of any triangle ABC being produc'd, the outward angle ACD will be greater then either of the inward and oppoſite angles CAB, CBA.
Let the right lines AH, BE a 10.1. &
1. poſt.
b 3.1.a biſect the ſides AC, BC; b produce EF = BE, and HI,
