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Question Video: Identifying Defining and Nondefining Attributes of Triangles Mathematics • 1st Grade

Fill in the blanks in the following sentences about triangles. All triangles _. [A] Have more than 3 sides. [B] Are yellow. [C] Have 3 sides. But only some triangles _. [A] Have 3 corners. [B] Are green. [C] Have 3 straight sides.

04:07

Video Transcript

Fill in the blanks in the following sentences about triangles. All triangles what. Have more than three sides, are yellow, or have three sides. But only some triangles what. Have three corners, are green, or have three straight sides.

This question is all about the 2D shape, the triangle. And we’re given some pictures to help us. We’re given two very short sentences to complete. Did you notice the main difference between them? There are two very small words, but they make a lot of difference. In the first sentence, it’s the word “all.” This means everything, doesn’t it, every single one. So to complete this sentence, we’re looking for a feature of triangles that every single triangle has. This is going to be one of the things that makes a triangle a triangle.

Now, the small word in our second sentence is the word “some.” This word is different because it means not all, part of the whole amount. And when we complete this sentence, we’re looking for a feature that not every triangle has in common, only some of them do. Let’s start with our first sentence then. All triangles what. Can we say that all the triangles in the picture and all the triangles we could ever draw have more than three sides? If we count the number of sides that our first triangle has, there are one, two, three.

We can use the picture to help us here. And we can say that all of the triangles in the picture do have three sides. And even if we were to draw some of our own, they would also have three sides. We can’t say all triangles have more than three sides, can we? We can’t even say some triangles have more than three sides. We’d have to say, no triangle ever has more than three sides.

Now, what about the color of these shapes? Can we say all triangles are yellow? Although one of our triangles in the picture is a yellowy-orange color, we know that triangles can be any color. They could be pink, green, or white, like in the picture. But they could also be blue stripy or shiny silver. I suppose we could say some triangles are yellow. The color of a triangle isn’t something that makes it a triangle. Now, we’re only left with one possible answer. All triangles have three sides. Well, we don’t need to think too much about this, do we? We’ve already talked about the fact that every single triangle has got three straight sides. We can say all triangles have three sides.

Now let’s think about our second sentence. But only some triangles what. Do only some triangles have three corners. Well, we can see on our first triangle in the picture that it does have three corners. In fact, so do all the others. This isn’t something that only some triangles have. This is something that’s true of every triangle. It’s one of those features that makes a triangle a triangle. We could actually use this phrase in our first sentence, “All triangles have three corners.” Let’s try our second phrase. Can we say only some triangles are green? Yes, we can, can’t we?

As we’ve said already, triangles can be any color. Of course, only some triangles are green, knowing the color of a shape doesn’t help us identify what sort of a shape it is at all. And let’s just check our last phrase. Only some triangles have three straight sides. Not at all. As we’ve found out already, all triangles have three straight sides. In this question, we’ve thought about the things that are always true of triangles and the things that are sometimes true. And this helped us complete the sentences. All triangles have three sides. But only some triangles are green.

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