( 5-2) 180 = 540 (degree)
But why is it so? Oh, that was the formula given by my Math teacher when I was in Secondary 2.
But why is it so? Oh, cause the number of non-overalp triangle you can draw from the same vertex of any polygon is always 2 less than the number of its sides. and each triangle has a total angles of 180 degree. or you can put a dot in the centre of the pentagon and draw 5 lines towards the 5 angles and form 5 triangles,
180 X 5 - 360 = 540 (degree)
All these methods suddenly came to my mind. I am trained to solve math questions through formula, traditional algoritthms. Not knowing that in order to deal with this problem, I have to reach level 2 - level 3 of Geometric thinkinf according to the van Hiele's 5 levels ( level 0- level 4) of the hierarchy model. At level 2 (informal deduction), the objects of thought are the properties of shapes and sometimes thinking about the relationship among these properties. and moving towards the beginning of level 3 ( formal deduction) which starts to look at the relationships among properties of geometric objects.
Van Hiele's model provides teachers with an insight of how children develop their geometric thinking and thus be able to use different strategies to help them move from one level to another. Chapter 20 demonstrates how a teacher should nurture his/her children in geometric thinking by asking appropriate questions and using guided activities to help children construct and internalize their own learning. It is a systematic and deliberate effort, it is the finest job of a Math teacher. To teach by not teaching .
Interesting website on geometry to share : http://coolmath.com/
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