Stage: 3 Challenge Level: 
Show that among the interior angles of a convex polygon there cannot be more than three acute angles.
Show that if a convex polygon has more than six sides, then at least one of the sides has an obtuse angle at both ends.
Visualising. Working systematically. Cubes. Creating expressions/formulae. smartphone. Angle properties of shapes. Generalising. Interactivities. Mathematical reasoning & proof. Squares.
Published September 1997.
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