Math Antics - Polygons - By
Transcript
00:03 | Uh huh . Hi there . Welcome to Math Antics | |
00:08 | so far in our series in geometry , we've learned | |
00:10 | about points , lines , planes and angles . In | |
00:14 | this lesson , we're going to learn about another important | |
00:16 | element of geometry . We're going to learn about polygons | |
00:19 | . You probably already know a lot about polygons because | |
00:23 | you see them all the time . Here are some | |
00:25 | common examples that you might recognize . These shapes are | |
00:29 | all polygons . That's because of polygon just means a | |
00:32 | multi sided shape and these shapes all have multiple sides | |
00:37 | . Okay , so that's a basic definition of a | |
00:39 | polygon . But to really understand what is a polygon | |
00:43 | and what is not a polygon . We need to | |
00:45 | learn about the specific properties that all polygons have in | |
00:49 | common . First , we need to know the three | |
00:51 | parts that make up all polygons . And these parts | |
00:54 | are sides vortices and angles . The sides are just | |
01:00 | the straight line segments that make up a polygon and | |
01:03 | the vertex is are the points where the sides intersect | |
01:07 | and the angles are formed by the intersecting lines . | |
01:10 | In fact in greek , the word polygon literally means | |
01:14 | many angles . So all polygons have sides advertises and | |
01:19 | angles . This polygon here has five sides , five | |
01:22 | verses and it forms five angles . The next thing | |
01:26 | we need to know about polygons is that they're closed | |
01:28 | shapes . Now , what does it mean for a | |
01:30 | shape to be closed ? You ask . Well it | |
01:33 | means that the sides are connected so that there are | |
01:35 | no gaps . The area inside , the shape is | |
01:38 | separated from the area outside the shape and there's no | |
01:42 | way to get from the inside to the outside without | |
01:44 | crossing the line . It might help to think of | |
01:47 | a close shape like a cage . If you put | |
01:50 | an ant inside the cage then there's no way for | |
01:53 | it to get out without crossing the line . But | |
01:56 | if the shape is open then there is a way | |
01:58 | out . So these are all examples of closed shapes | |
02:02 | . And these are all examples of open shapes . | |
02:04 | And the important thing to remember is that a polygon | |
02:07 | must be closed . And the last thing we need | |
02:10 | to know about polygons is that they're two dimensional or | |
02:13 | flat shapes . And that means that all the vertex | |
02:16 | is must lie on the same plane . If any | |
02:19 | one of the vertex is were to move forwards or | |
02:22 | backwards so that it wasn't on the same plane as | |
02:24 | all the other vertex is . Then it wouldn't be | |
02:26 | a flat shape anymore . Flat shapes are also called | |
02:29 | cleaner shapes because all of their points are on the | |
02:33 | same plane . And even though polygons themselves can't be | |
02:36 | three D shapes , you can use polygons to make | |
02:39 | three D shapes like a box . For example , | |
02:42 | the box is not a polygon , but each of | |
02:45 | its flat sides is a polygon . All right then | |
02:50 | we now have a specific definition of a polygon . | |
02:53 | The polygon is a multi sided shape that has sides | |
02:56 | , verte sizes and angles . A polygon is a | |
02:59 | closed shape and a polygon is a two dimensional or | |
03:03 | a flat shape . And now that you know that | |
03:06 | it's time to play polygon or not a polygon . | |
03:10 | Now here's your host , me . Thank you . | |
03:14 | Thank you . All right now the rules of the | |
03:17 | game are simple . I'm gonna show you a shape | |
03:19 | and you tell me if it's a polygon or not | |
03:22 | a polygon , are you ready to play ? Our | |
03:26 | first shape is a square , is a square polygon | |
03:31 | . Yes square has four sides and four advertises . | |
03:35 | And it's a closed two D . Shape . So | |
03:37 | it is a polygon . And next we have but | |
03:43 | not exactly sure what to call this . But is | |
03:46 | it a polygon , nope , it's close but because | |
03:49 | it's an open shape , it can't be a polygon | |
03:53 | . All right . What about this one , polygon | |
03:56 | or not polygon , yep . It is a polygon | |
04:01 | even though the sides aren't all the same length . | |
04:03 | It is a closed two D . Multi sided shape | |
04:06 | . In fact if you count you'll see that . | |
04:08 | It has seven sides . What about this one ? | |
04:14 | Is a circle of polygon ? Well it is a | |
04:17 | closed two D . Shape but how many sides does | |
04:21 | it have ? Now ? That's the problem . A | |
04:24 | circle doesn't have any straight sides advertises or angles . | |
04:28 | It's a curved shape . So it's not a polygon | |
04:31 | . Next we have a star shape just like me | |
04:35 | . Is it a polygon , yep , it has | |
04:39 | straight sides advertises and it's a closed two D . | |
04:43 | Shape . That means it's a polygon . And what | |
04:47 | about this one ? Right , you are . This | |
04:50 | is not a polygon , It's a dog . Uh | |
04:55 | Here's an interesting one . It's a closed two D | |
04:58 | . Shape that does have straight sides and vortices . | |
05:01 | But it also has this curved part here . Can | |
05:05 | it still be a polygon with that curve there ? | |
05:07 | No the curved part disqualifies it as a polygon polygon | |
05:13 | has to have only straight sides . So this is | |
05:18 | not a polygon . And what about this guy here | |
05:21 | ? Is this a polygon ? Well it is just | |
05:23 | straight lines but two of those lines cross and if | |
05:27 | any lines cross it can't be a polygon . Plus | |
05:30 | he has this big open in here . So this | |
05:32 | guy is definitely not a polygon . And last of | |
05:36 | all , what about this one ? Right . You | |
05:38 | are this is not a polygon because it's a three | |
05:41 | D . Shape . It's made from polygons . But | |
05:44 | the whole shape is not a polygon itself . Well | |
05:48 | that's all the time we have for this week , | |
05:50 | join us next week as we decide is it bigger | |
05:53 | than one ? Okay so after playing that game you | |
05:58 | should have a really good idea of what a polygon | |
06:00 | is and what it is . Not . The last | |
06:02 | thing I want to mention is that some polygons have | |
06:05 | special names depending on how many sides they have . | |
06:08 | Here is a list of the most important ones to | |
06:11 | know . three sided polygons are called Triangles . Triangles | |
06:15 | are so important in geometry that they'll get a whole | |
06:18 | video of their own foresighted polygons are called quadrille laterals | |
06:24 | , wow . Now that's a fancy math word But | |
06:27 | it helps if you just remember that the first part | |
06:29 | quad means four quadra laterals are shapes like squares , | |
06:34 | rectangles and parallelogram . They'll also get a video of | |
06:38 | their own five sided polygon are called Pentagon's six sided | |
06:43 | polygons are called Hexagons . An eight sided polygons are | |
06:47 | called Octagon , by the way , polygons that have | |
06:51 | 568 or however many sides like this are called regular | |
06:55 | polygons . If all of their angles are equal and | |
06:58 | irregular polygons , if their angles are not equal , | |
07:02 | of course there are a lot more polygons than that | |
07:05 | , but you probably won't need to know their names | |
07:08 | as long as you know what polygons are and how | |
07:11 | to identify them , then you're ready to move on | |
07:14 | . The exercises for this section are pretty easy . | |
07:17 | So no excuses . Good luck . Thanks for watching | |
07:20 | Math Antics and I'll see you next time learn more | |
07:24 | at Math Antics dot com . |
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