A diagonal is a line segment that connects non-adjacent vertices in a polygon. How many diagonals does an octagon have?	Choices
A) 20 B) 40 C) 60 D) 90 E) 80
Select one vertex and you can draw 5 diagonals.   If you draw 5 such diagonals for each of the 8 vertices, you will draw a total of 5 × 8 = 40 diagonals. But you actually draw each diagonal twice, once from each of its ends. Therefore, there are a total of 40 ÷ 2 = 20 different diagonals   correct answer 20
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A diagonal is a line segment that connects non-adjacent vertices in a polygon. How many diagonals does an octagon have?