Start with smaller number sided polygons (triangle, square, pentagon, …(Yellow) Start with hexagon (Red) How many diagonals does an octagon have? Count diagonals systema6cally Use different colors (Red) Might be beFer to put a leFer at each vertex I wonder if there is a paFern… (Red) Draw diagrams and think (Red) 4 diagonals
5 x 8 = 40 (diagonals)
Non- systematic
counting
Counting diagonals using
different colors
5th Grade Lesson: Finding Number of Diagonals of an Octagon