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Regular decagon | |||
---|---|---|---|

Edges and vertices | 10 | ||

Schläfli symbols | {10} t{5} | ||

Coxeter–Dynkin diagrams | >- | Symmetry group | Dihedral (D_{10}) |

Area (with t=edge length) | $A\; =\; frac\{5\}\{2\}t^2\; cot\; frac\{pi\}\{10\}$$=\; frac\{5t^2\}\{2\}\; sqrt\{5+2sqrt\{5\}\}$ $simeq\; 7.694208843\; t^2.$ | ||

Internal angle (degrees) | 144° |

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

- $$

& simeq 7.694208843, a^2.end{align}

- Complete steps 1 though 6 of constructing a pentagon.
- 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.
- 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).

- Definition and properties of a decagon With interactive animation

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Last updated on Sunday September 28, 2008 at 19:16:14 PDT (GMT -0700)

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Last updated on Sunday September 28, 2008 at 19:16:14 PDT (GMT -0700)

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