A diagonal is a line that connects two non-adjacent vertices of a shape. A decagon has 35 diagonals in total.
A diagonal goes from one corner to another corner of the shape, without following a side. In the image, the diagonals are shown in teal:
There is a formula that works for any polygon to count the number of diagonals:
For a decagon: n = 10, which gives D = 35 diagonals.
Yes! The formula works for any convex polygon. For example, a pentagon (n = 5) has 5 diagonals, and a hexagon (n = 6) has 9 diagonals.
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