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## Basic geometry and measurement

### Course: Basic geometry and measurement>Unit 4

Lesson 4: Classifying geometric shapes

# Classifying shapes by lines and angles

Lindsay classifies a shape based on hints about its sides and angles.

## Want to join the conversation?

• Sal is a very talented person. He has very smart brains and is very clear on what he's trying to say. YAY FOR SAL!
(21 votes)
• the feeling when you know the answer the hole time but you still need to watch the vid
(18 votes)
• exactlly
(1 vote)
• how do you know if that's the shape?
(11 votes)
• Hi mathews.bentina, you can tell that that's the shape by the symbols they give.
(5 votes)
• Where is sal?!
(9 votes)
• Where is salllll
(3 votes)
• the comments are so old.
(8 votes)
• What happened to Sal!?🫢
(6 votes)
• how did the small triangle be obtuse
(6 votes)
• Do any of you have a website for an online protractor?
(2 votes)
• What is the shape the has the most sides?
(3 votes)
• Shapes (more specifically polygons) can have multiple sides as their name suggest (poly - many; gons - sides). We cannot define a shape with the most sides, because there will always be a shape with one side more.

Hope that helps.
(3 votes)
• This is the first time i remember that there is a female voiceover
(2 votes)
• There are a few of those. It's a bit of a surprise when you are used to Sal Khan, but it's still nice.
(4 votes)

## Video transcript

- [Voiceover] Which shape matches all three clues? So here we have three clues and we want to see which shape down below matches all three of these statements. So let's start with the first clue. The first clue says the shape is a quadrilateral, quad meaning four-sided. So looking down here at our shapes, let's see which ones match that first clue. Shape one has one, two, three, four sides. So it is a quadrilateral. Shape two has one, two, three, four sides. So also a quadrilateral. Shape three has one, two, three, four, five, six sides. So it is not a quadrilateral. It's a six-sided shape or a hexagon. So we can rule that one out. It doesn't match clue one so there's no way it can match all three clues. And finally shape four has one, two, three, four sides again so it is also a quadrilateral. So after clue one, we still have three possible answers. This first shape, the second shape, and the fourth shape all match clue one, they're all quadrilaterals. Looking at clue two, it says our shape has no right angles. Right angles are also 90 degree angles. Right angles are 90 degree angles and they look something like this and we often see them marked with a square in the middle because they are sort of like square angles. We can create a square from the opening that they form, that these angles form. So this is a right angle. Looking now down at our shapes, we can see right away on shape one has two right angles. There's a square corner and another square corner. So this has right angles, but the shape we're looking for has no right angles so we can rule this shape out. Shape two does not have any right angles. These are not squared off corners. And same with shape four, no right angles. So both of those still match both clues one and two. So we have two shapes left. They're both quadrilaterals and they have no right angles. And finally our last clue, the shape has four sides, we knew that 'cause it was a quadrilateral, and those sides are of equal length. That means each of the sides is the same length. Looking at this first one that we have left, shape two, it looks like these sides on the ends are shorter than the sides going up and down. So it looks like they are not equal length. So we can rule this one out. But let's be sure this last one works. Here the sides all look like they're the same length, but the way we can know for sure that they are is these tick marks. Any time you have these marks, it's saying that any side that has the same amount of marks is the same length. All four of these sides have exactly one tick mark so they are all equal in length. So shape four matches all three clues. It is a quadrilateral, there are no right angles and it has four sides of equal length. So shape four is our answer.