# Classifying Triangles 4th or 5th grade

Discussion in 'Elementary Education' started by Upsadaisy, Jul 1, 2012.

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Jul 1, 2012

NAMING TRIANGLES TWO WAYS

Triangles can be identified by their sides and by their angles. We give them their names by measuring the length of the sides with a ruler, and measuring their angles with a protractor. This is called classifying triangles.

Every triangle will have two names. One is based on the length of its sides. One is based on the measurement of its angles. Here is how we decide on their names:

Length of Sides
Equilateral triangle - has three sides with the same length.
Isosceles triangle - has two sides with the same length.
Scalene triangle- has no sides with the same length.

Measurement of the Angles
Right triangle - has one right angle.
Obtuse triangle - has one obtuse angle.
Acute triangles - has at least two acute angles.

So, a triangle may be classified, or named, as: right scalene acute equilateral acute isosceles obtuse scalene obtuse isosceles

Then, I gave them a handout with various triangles shown. I had them use the triangles on the handout, then measure and put the information on this chart.

CLASSIFYING TRIANGLES

For each TRIANGLE:

LENGTH OF SIDES _____
MEASURE OF ANGLES _____
2 NAMES _____, _____

3. ### AliceaccMultitudinous

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Jul 1, 2012

Just one little change I would recommend.

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Jul 1, 2012

Sounds similar to what we do. Some students have trouble with the idea of two different names, so we liken it to people having first and last names.

5. ### callmebobEnthusiast

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Jul 1, 2012

I have taught these triangles every year in 4th grade. What is the question in regards to these triangles?

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Jul 1, 2012

Ditto to the suggestion of likening it to a person having a first name and a last name. I often pick two students who have the same first name (i.e. "If your name is Brian, stand up") and talk about how if I called on Brian, I really could be referring to either one since they are both Brian. However, if I want to be more specific and call on Brian Johnson, now they know I am talking about that one specific student...

Another activity that really helps is having students actually draw triangles under different sets of constraints. This helps them understand the difference between the "side length" names and the "angle measurement" names. Drawing them correctly is MUCH harder for them than just classifying, but I feel that it is worth the effort.

For example:

- Draw an acute triangle. Compare drawings with partner. How are they the same/different? Use a protractor to measure the angles on your partner's triangle. Is their triangle really an acute triangle? Justify your answer.
- Now draw an acute triangle that is also scalene. Compare with partner. Use a ruler to measure the side lengths.
- Then I have volunteers bring their examples up and put them on the Elmo and we use a protractor and ruler to determine if theirs is really, TRULY, an acute scalene triangle. They tend to not be very precise when drawing the angles.

I always end by having them try to draw an obtuse equilateral triangle, or even just a triangle with two obtuse angles

7. ### CFClassroomConnoisseur

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Jul 1, 2012

Am I missing something? Is there a question? I'm confused.

But, despite my confusion I wanted to ask if you are assuming that they know they properties of a triangle and correct vocabulary (i.e. vertex/vertices) prior to teaching the above.

We cover it in 3rd, but I just wanted to make sure you had thought about the background content.

8. ### giraffe326Virtuoso

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Jul 1, 2012

No question. Upsadaisy posted several lesson ideas. This is one of them

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Jul 1, 2012

I responded to someone's PM request for some files and was going through old stuff, so I decided just to post some things that others might find useful as they gear up for next year.

Thank you, Alice; you are absolutely correct.

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