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Intro to quadrilaterals

CCSS.Math:

Video transcript

what I want to talk about in this video is shapes with four sides and the mathy word for shapes with four sides is quadrilateral quadrilateral and anytime you see quad as part of a word it's a good it's a it's a good sign that you're dealing with the number four somehow so quadrilateral is something that has four sides so that is a quadrilateral this is a quadrilateral this is a quadrilateral they all have four sides this is a quadrilateral even this is a let me make it look leaving weird or even this is a quadrilateral so what's not a quadrilateral well a triangle would not be cuadrado it has three sides one two three so let's cross that out a pentagon that has five sides that would not be a quadrilateral it has one two three four five sides a circle that has I guess you could say no sighs it's just one big curve it's a circle that had that's not going to be a quadrilateral if you had six sides seven sides 100 sides none of that is going to be a quadrilateral so now let's think about the different types of quadrilaterals or the different categories of quadrilaterals so one is the parallelogram so a parallelogram is a quadrilateral and as we learn more math we'll learn four we'll learn other ways of thinking about this it's a quadrilateral where opposite sides are parallel and parallel is just another way of saying that they're going in the same direction so what do I mean by that so something like this something like this would be a parallelogram why because this side is opposite to this side and they're pointed in the same direction they're going they're going if I were to draw an arrow if I were to draw an arrow here those arrows are pointed in the same way so those two sides are pointed are parallel is the word we say and these two sides these two sides right over here are parallel so this is a parallelogram so what are other examples of parallelogram well even your classic square even your classic square is a parallelogram and we'll talk more about what makes a square special it's a special type of parallelogram because this side is going in the same direction as that side and this side and this side whoops let me do that in yellow and this side is parallel to that side so what's not a parallelogram well something like something like this would not be a parallelogram you might say wait I see two opposite sides are parallel you might say look this is parallel to this but then you would see that this is not parallel to this one way to think about some things that are not parallel is if the lines kept going they would cross each other at some point while these lines these lines right over here they're never going to cross each other so this one right over here is not a parallelogram it has one set of opposite sides being parallel but not the other another example of something that is not a parallelogram would be this one right over here because none of the opposite sides are parallel so parallelogram opposite sides are parallel so now let's talk about let's talk about more types of four sided shapes or quadrilaterals so the next one we'll talk about is the rhombus so the rhombus is a type of parallelogram the opposite sides need to be parallel but that's not that's by itself that doesn't make it a rhombus the opposite sides going to be parallel and all the sides have to be equal so for example this that I'm drawing that is a parallelogram but it is not a rhombus it's a parallelogram because that side these opposite sides are parallel if you they kept going they would cross each other and these two so opposite sides are parallel so it's a parallelogram but it's not a rhombus because the blue sides are longer than the yellow sides so that is not a rhombus a rhombus would have to look like this a rhombus would have to look like that so opposite sides are parallel and all the sides are the same length and now you might say well maybe a square is a rhombus and I want you to think about that is a square or rhombus are all the sides the same length and are the opposite sides parallel well we already said that the opposite sides of a square are parallel square is a parallelogram and all the sides of a square are the same length so a square is a rhombus so one way to think about rhombuses or rhombi is they're squares and you could kind of view them as kind of pushed over version of squares if a square was moving really really fast in a cartoon that's what my brain thinks of when I think of a rhombus so now let's think of a rectangle and you might have heard the word rectangle in the past but let's think a little bit more about what makes a rectangle so a rectangle is going to be a parallelogram but that by itself does not make it a rectangle so for example this right over here is a rectangle why is it well it's definitely a parallelogram this side and that side are parallel they'll never intersect and this side and this side are parallel they're never they're never going to intersect if you kept going on and on and on or they're never going to cross each other but what makes it a rectangle it's definitely a parallelogram but what makes it why do we use the word rectangle well one way to think about it is the way that they come together at the corners so in a rectangle the things come in to I guess you could call them square corners and that's called a right angle that's called a right angle right over there so this is what makes a rectangle it's a parallelogram where all the corners are right angles you could put a little square there if you want think about it that way so for example this right over here would not be a rectangle why because you can't if you put a square here notice that does not a square doesn't fit in the corners the way that it fits right over here that you have the square does not fit over here this is a parallelogram but not a rectangle a rectangle is a parallelogram that has square corners but what about our square is a square or rectangle well let's draw it out well let's think about it a square opposite sides are parallel we've already said it's a parallelogram and a square has the corners are square that's that's when people say make a square corner that's where it comes from the corners are square they are right angles so the square is a rectangle so the square is a really interesting quadrilateral because the square falls into all of these categories the square a square is a square it's a rhombus it's the type of rhombus where the corners are right angles or you could say where the corners are square this one right over here is not a square this one is squared they're both rhombuses or they're both rhombi a square is also a rectangle up it's a parallelogram where the corners are right angles where they are square a square is definitely a parallelogram and everything we've talked about is a quadrilateral