A diagonal line of a polygon is a line that joins any two vertices not already joined by a side.
A polygon with n sides has n(n-3)/2 diagonals
→ a decagon has 10(10-3)/2 = 10 × 7 ÷ 2 = 35 diagonals
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A decagon need not have any lines of symmetry. It can also have 1 or 10 lines of symmetry.
A decagon need not have any lines of symmetry. It can have 10.
Ten.
6
A decagon is a 10 sided polygon Exterior angles add up to 360 degrees Interior angles add up to 1440 degrees It has 35 diagonal A decagon can have a regular or an irregular shape