Detailed definition
Understanding Decagon
Decagon is a polygon with ten sides. A decagon is a polygon with ten sides. Like all named polygons, the word decagon tells you the side count before it tells you anything about regularity or symmetry.
A regular decagon has equal sides and equal interior angles of one hundred forty-four degrees. Its exterior angles are thirty-six degrees, which connects it nicely to pentagon-based angle patterns in the regular case.
This polygon is useful because the ten-side count leads to rich but still manageable combinatorial facts such as many diagonals and a large interior angle sum, while staying close to familiar decimal counting.
Key facts
Important ideas to remember
- A decagon is a polygon with ten sides.
- A decagon has ten sides, ten vertices, and an interior angle sum of one thousand four hundred forty degrees.
- Each interior angle of a regular decagon measures one hundred forty-four degrees.
- A decagon has thirty-five diagonals in total.
Where it is used
Where decagon shows up
- Use decagon naming in polygon classification and side-count exercises.
- Use regular-decagon angles in symmetry and angle-measure problems.
- Use the shape to compare polygon diagonals and interior sums across different side counts.
Common mistakes
What to watch out for
- Do not mix the regular decagon's angle values into irregular decagon cases automatically.
- Do not lose count in a shape with many short sides and many diagonals.
- Do not confuse ten sides with ten diagonals; those are different counts entirely.