median
don steward
mathematics teaching 10 ~ 16

Wednesday, 30 March 2011

nonagon appreciation society

the nonagon is a fine shape to explore

establish that any pair of diagonals must meet at either 100 or 120 or 140 degrees

find 4 different isosceles trapeziums (trapezoids) and identify the angles within each of them




prove that there are 7 different triangles that can be drawn, connecting vertex to vertex

this work can use the interior angles of regular polygons
or could establish e.g. that there are 140 degrees inside each vertex of a regular nonagon:


this could also be used to establish that the interior angle is 140 degrees

or you could find the angles in the arrowheads


















in terms of lengths, establish that
a + b = c

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