Students will learn what a diagonal of a polygon is, and how to derive the formula for the number of diagonals in an \(n\)-sided convex polygon. That is, \(n(n - 3)/2.\)
Number of Diagonals in a Polygon by Brightstorm
This topic is not covered by the Common Core, nor Khan Academy.
Next, give your students this challenge:
Remainders of Two by MAA
Conclude by leading this investigation:
Skinny Man Tango (area, algorithm)