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# Recognizing shapes

CCSS.Math:

## Video transcript

I have a bunch of shapes here let's think about what they are so this first shape here you probably recognize it it's the shape of the moon in the sky at least on a full moon and we call it a circle now what makes it a circle well when you get further in math we come up with fancier ways to define a circle but one way to think about it is if we take the center of the circle and if we go across we go from one side of the circle to the other side of circle through the center that's always going to be the same length so that's the same length as this as this as long as we go to the center of the circle as that now if that's a circle what would something like this be what you might call this an oval and all all circles are ovals but this oval is not a circle because if you have its center say right over there this distance going in that direction is going to be much shorter or just shorter than this distance right over here so this one right over here is not a circle this one is now what about this shape over here that has three sides one two three you could also say it has three corners one two three well if you have three sides we call that a triangle tri angle whenever you see this tri right over here that's a good sign that you're dealing with the number three this is a triangle has three sides now what about these shapes over here these shapes are interesting how many shapes so how many sides do these shapes have well if you count them you see that this one up here in purple has one two three four sides this one has one two three four sides this one has one two three four sides this has one two three four sides so they all have four sides so our name for any shape that has four sides is quadrilateral kua drei quadrilateral quadrilateral and when you see this at the beginning of the word that's a pretty good sign that you're dealing with the number four four sides four sides that's what quadrilateral means but these are all different special cases of quadrilaterals and actually you could even have a quadrilateral that looks like this you could even have a quadrille that looks like this one two three four sides as long as it has four sides it's a quadrilateral let's think about each of these so this shape right over here what you might see is the corners the corners all come in sometimes this is called square or sometimes you could call it a right angle so and notice I could put a little small squares here so if all four corners are square or they are all come in at a right angle like this then you're dealing with a rectangle you are dealing with a rectangle and so just to be clear this down here is not a rectangle notice this corner right over here if I try to put a little square here it would either look like this so it doesn't it doesn't the two sides aren't on two sides of the square or it would look like or it would look like this so this is not a square corner and neither there is this or neither is this so this is not a rectangle all four corners need to be square this one also is not a rectangle notice the corners are not the corners are not right angles so this isn't directed rectangle this isn't directing what about this well I can do that I can put little squares I could put a little squares in the corner or I could see that they are all right all the corners are right angles so this actually is a rectangle as well so these are both these are both rectangles now you might recognize this purple one on the left is a special type of rectangle not only are all of the corners square not all do they have these right angles but all the sides are the same length or at least it looks like it from this picture this side is the same length as this side the same length as that side same like this that side so if all the sides are the same length in all the corners are are square or they have right angles well then we call it a square so this right over here is a this right over here is a square special type of rectangle this one not all the sides are the same this one all the sides are the same now what if we go down here it looks like all the sides are the same 1 2 3 4 but it doesn't necessarily R it wouldn't fit perfectly if I try to put a little air here doesn't fit perfectly these aren't right angles so if all four sides are the same and that's all we know about it we call it a rhombus we call it a rhombus so you might be saying wait wait the square all four sides the same is that a rhombus yes it is so the square is a rectangle it's a rectangle and and it is a rhombus so this last shape here this last quadrilateral what's interesting about it is you have two of its sides going in the same direction so this one right over here notice what I mean by the same direction and sometimes this is called parallel if I draw two lines here these two lines are never going to cross each other so these two lines are parallel if you have opposite one pair of opposite sides that are parallel we call them trapezoids we call them trapezoids notice the other lines the other opposite sides these will cross these will cross eventually so that right over there is called a trapezoid