An elementary treatise on modern pure geometry (1893)
Lachlan, Robert · London, New York, Macmillan and Co. · leaf 34
areconnected by the relation sin BOG. sin ADD + sin GO A . sin BOD + sin AOB. sin GOD = 0. … Let any straight line be drawn cutting the rays of the pencilin the points A, B, G, D. Then, by § 25, we have BC.AD + GA.BD + AB.GD = 0. But if ON be the perpendicular from the vertex of the pencilon the line AB, we have, from § 22, NO.AB = OA.OB. sin AOB,and similar values for NO. AD, NO. CD,…
Geometry
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