| Activity Outcome | Investigating the number of diagonals that can be drawn inside a polygon. |
| MTS Set | 6
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| NSW Curriculum | |
| Topics | 2D Shape
Reason Geometrically
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| Keywords | Pattern Searching, Pattern Making, Pattern, 2D Shape |
| Grouping | Whole class and learning pairs. |
| Resources | Not applicable |
| Lesson Notes | - Direct pairs to the Investigation and ask: Recently we investigated the number of diagonals that could be drawn from one vertex of a polygon. (See Activity 384.) How is this investigation similar?
- Ask: What is the key information we need to find for this investigation? (Number of diagonals that can be drawn inside different polygons.) How will we collect the information? (Draw polygons and diagonals.) How will we record the data we collect? (Make a table of polygons, sides and diagonals.) How much data should we collect? (Data from at least 4 or 5 polygons.) What will we be looking for after we have collected the data? (To see if there is a pattern we can follow to know the number of diagonals inside a decagon.)
- Direct pairs to carry out the Investigation starting by describing their plan (Strategy). Also direct pairs to keep a record of their progress using the reflection table on the activity sheet.
- (Reflection) Move around the pairs and ask the focus-inquiry questions as above.
- Provide pairs with the opportunity to share responses.
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| Reflections | See Lesson Notes.
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| Integration Links | Not applicable.
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| Internet Links | http://www.math.com/school/subject3/lessons/S3U2L3GL.html Excellent site for background material on geometric ideas.
Suitable for teachers and year 5 up.
http://www.aaamath.com/geo318-polygons-sides.html Interactive activity where students recognise the features of polygons from triangles to decagons.
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| Answers | Polygon Number of Sides Number of Diagonals
Triangle 3 0
Rectangle 4 2
Pentagon 5 5
Hexagon 6 9
Heptagon 7 14
Octagon 8 20
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