a regular decagon

In geometry, a decagon is any polygon with ten sides and ten angles, and usually refers to a regular decagon, having all sides of equal length and all angles equal to 144°, therefore making each angle of a regular decagon be 144°. Its Schläfli symbol is {10}. The area of a regular decagon of side length a is given by Image File history File links Decagon. ... Image File history File links Decagon. ... Table of Geometry, from the 1728 Cyclopaedia. ... Look up polygon in Wiktionary, the free dictionary. ... An angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle. ... A regular pentagon A regular polygon is a simple polygon (a polygon which does not intersect itself anywhere) which is equiangular (all angles are equal) and equilateral (all sides have the same length). ... In mathematics, the Schläfli symbol is a simple notation that gives a summary of some important properties of a particular regular polytope. ...

Constructing a decagon

A regular decagon is constructible with a compass and straightedge. In mathematics, there are several notions of constructibility: a point in the Euclidean plane that can be constructed with unruled straightedge and compass. ... Creating a regular hexagon with a ruler and compass Construction of a regular pentagon Compass and straightedge or ruler-and-compass construction is the construction of lengths or angles using only an idealized ruler and compass. ...

1. Complete steps 1 though 6 of constructing a pentagon.
2. Extend a line from each corner of the pentagon through the center of the circle made in step 1 of constructing a pentagon to the opposite side of that same circle.
3. The five corners of the pentagon constitute every other corner of the decagon. The remaining five corners of the decagon are those points where the lines of step 2 cross the original circle (but not a pentagon corner).

Look up pentagon in Wiktionary, the free dictionary. ... Circle illustration In Euclidean geometry, a circle is the set of all points in a plane at a fixed distance, called the radius, from a fixed point, the centre. ... Look up pentagon in Wiktionary, the free dictionary. ...

See also

• decagonal number
• Gambrel

A decagonal number is a figurate number that represents a decagon. ... A gambrel is a symmetrical two sided roof with two slopes, the upper slope being less steep. ...

External links

• Eric W. Weisstein, Decagon at MathWorld.
• Definition and properties of a decagon With interactive animation

Dr. Eric W. Weisstein Encyclopedist Dr. Eric W. Weisstein (born March 18, 1969, in Bloomington, Indiana) is a noted encyclopedist in several technical areas of science and mathematics. ... MathWorld is an online mathematics reference work, sponsored by Wolfram Research Inc. ...