Friday, March 13, 2009
Geometry Training: Geometry Cabinet Triangles
The Triangle drawer in the Geometry Cabinet
At the Elementary Level triangles are first presented to a first grader without ever talking about degrees and by second or third year we go into degrees. The children learn the terminology acute, obtuse, and right angles but never look at the degrees at the beginning. This was hard for me to get used to. As adults we want to go straight into talking about degrees!
The first presentation is triangles by sides.
Start with the equilateral triangle, the isosceles and finally scalene.
"This is an equilateral triangle" "What do you notice about this triangle"
Rotate triangle in its frame, it fits in its frame no matter what.
Reverse the triangle and attempt to pass the triangle through the frame. What do you observe?
Discuss the etymology of the word.
The second presentation is to present the triangles by angles.
Start with the right scalene triangle. 'There are two ways to describe triangles, one by looking at its sides and the other by looking at its corners.
"A triangle with one square corner is called a right triangle." Put the triangle inside the square frame to show this. Now show the plastic measuring angle that comes with the geometry stick box or you can use a protractor like in the picture above. "This special triangle has a corner marked in red because it is a right angle" "We can use it to check for right angles". If you are using a protractor, you will need to paint the corner red!
"This is an obtuse triangle, it has no right angles" Show with the measuring angle. It has one angle larger than a right angle." Measure the triangle against the measuring angle to prove this.
Lastly is the acute triangle.
You can distribute triangles from the Detective Triangle Game so the children can classify.
Here is the Detective Triangle Game.
Lastly is to identify all of the angles by their sides AND their angles. You will work with the triangle work chart below and the triangle drawer.
This chart has SIDES at the top (equilateral, isosceles, scalene) and ANGLES on the left side of the chart (obtuse, acute, right). So, we place the isosceles, acute triangle in its correct place, etc..
Now the children are ready to play the detective game. The game comes with these strips of paper that children use independently to find the triangle described. Example: "the large yellow right angle"
Here are the descriptions of the triangles. You have small, medium and large triangles that are blue, yellow and red. After the children play this game a few times they get it! You may want to begin by having only a few out so that it does not become so overwhelming. Maybe all large triangles of the three different colors.