Elements of geometry for the use of schools (1854)
Ireland. Board of National Education · Dublin : A. Thom · leaf 72
I B will be an isosceles triangle.And as the vertical angle is of 60 degrees,each of the other two angles will also be of60 degrees, which is the half of 120. Thetriangle AIB will consequently be equilateral(Art. LXX.) A B must therefore be equal toa radius of the circle. Hence it is clear thatin… … M- LXXII. Having described the hexagon AB CDE F,it will be easy to describe a dodecagon orpolygon of twelve sides.The half of Divide the arc A KB, or the angle A IB, an angle at the centre of mto two equal parts, and AK, the chord of a hexagon, 13 x x one of the half the arc A KB, will be one of…
Geometry
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