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Angle trisection is the construction, using only a straightedge and a compass, of an angle that is one-third of a given arbitrary angle. This is impossible in the general case. For example, the angle 2 π /5 radians (72° = 360°/5) can be trisected, but the angle of π /3 radians (60°) cannot be trisected. [8]
The angle π / 3 radians (60 degrees, written 60°) is constructible. The argument below shows that it is impossible to construct a 20° angle. This implies that a 60° angle cannot be trisected, and thus that an arbitrary angle cannot be trisected. Denote the set of rational numbers by Q.
Proof: Construct a sphere on top of each circle and then construct a plane tangent to these three spheres. The plane intersects the plane that the circles lies on at a straight line containing P 1, P 2, and P 3. These points are also the centers of homothety for the circles that they were derived from. [4]
In graph theory, a planar graph is a graph that can be embedded in the plane, i.e., it can be drawn on the plane in such a way that its edges intersect only at their endpoints. In other words, it can be drawn in such a way that no edges cross each other. [1] [2] Such a drawing is called a plane graph, or a planar embedding of the graph.
Bisection of an angle using a compass and straightedge. An angle bisector divides the angle into two angles with equal measures. An angle only has one bisector. Each point of an angle bisector is equidistant from the sides of the angle. The 'interior' or 'internal bisector' of an angle is the line, half-line, or line segment that
7a. Construct a vertical line through F. It intersects the original circle at two of the vertices of the pentagon. The third vertex is the rightmost intersection of the horizontal line with the original circle. 8a. Construct the other two vertices using the compass and the length of the vertex found in step 7a.
The following construction is a variation of H. W. Richmond's construction. The differences to the original: The circle k 2 determines the point H instead of the bisector w 3. The circle k 4 around the point G' (reflection of the point G at m) yields the point N, which is no longer so close to M, for the construction of the tangent.
This type of construction is called a neusis construction. It is also constructible with compass, straightedge and angle trisector . The impossibility of straightedge and compass construction follows from the observation that 2 cos 2 π 7 ≈ 1.247 {\displaystyle \scriptstyle {2\cos {\tfrac {2\pi }{7}}\approx 1.247}} is a zero of the ...