WEBVTT

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In this video, I really wanted to introduce

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you to some terminology for some basic angle types

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and terminology. I wanted to introduce you to are

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acute angles, right angles, and obtuse angles.

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I think when we go through these,

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it will be pretty self-explanatory.

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And an acute angle is an angle --

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let me just draw them first

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then you might,

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you might,

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it might start to make sense.

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So an acute angle

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will look something like that.

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I draw two rays

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coming from a common point.

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I could also --

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so the acute angle could be this angle right over here.

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I could also draw an acute angle;

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maybe an angle that is formed from an intersection of two lines,

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so this angle would be acute,

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and so will this angle.

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They're both acute angles.

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We are going to see acute angles as ones

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that are --

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that since I haven't defined right angles yet.

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They are narrower,

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so we are going to see that they are

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smaller than right angles.

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Right angles are when the rays

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or the lines are going, oh

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I guess, I don't want to use the word "right"

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in my definition.

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They are kind of

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if one is going horizontal

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then the other one will be going vertical.

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so let me draw with rays first

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so the right angle

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this one is going from the left to the right

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and the other ray is going from the bottom

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to the top

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this angle right over here

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is a right angle

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and I could label it like that

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but as a traditional angle

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but the general,

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the general convention for labeling right angles

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is to put a little,

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a kind of a half of a box over there.

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That tells me that this is a right angle

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or, that if this is going left to right

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this is going perfectly top to bottom

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that this is a no way kind of

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that this is a completely,

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I guess the best way to think about it

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why it's called right

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is that this ray is completely upright

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compared to this ray over here

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let me draw with some lines

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if I have one line like this

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and I have another line like that

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a right angle over here

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actually all of these would have to be

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right angles

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it would mean that this line

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is completely,

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if this line were the ground,

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this line is completely upright

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relative to this line over here.

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so either these,

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so that is what a right angle means

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so now that we defined right angle

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I can give you another definition for acute angle

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so an acute angle has a measure

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or it's smaller than a right angle

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so you learn about radients and degrees

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which are different ways to measure angles

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so you'll see that a right angle

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can be measured as 90 degrees

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this over here is less than 90 degrees

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so this is less than 90 degrees.

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and one way to conceptualize this is

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that this angle,

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it's opening is smaller

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it's more narrow,

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it's lines are,

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you would have to rotate one line

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less to get to the other line

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then you would over here.

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here, you would have to move

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all the way over there

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here you only have to move it a little bit

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so the acute angle is less than a right angle

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so you might imagine already

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what an obtuse angle is

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it is greater than a right angle

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so let me draw a couple of examples

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of obtuse angles

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so an obtuse angle might look like

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let me get it a little clearer

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might look like that

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if it was a right angle,

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then this line over here

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would be,

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would look something like that

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it would be completely upright

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relative to this, if this were the ground.

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but we don't see that

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this orange ray over here is actually

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opened out wider

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it's opened up wider

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so it is obtuse.

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it is obtuse

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so this kind of comes from the actual

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everyday meaning

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acute means very sharp or very sensitive

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obtuse means not very sharp or not very sensitive.

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you could imagine this looks like a sharp point

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or it's, it's not opening up much.

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so maybe it's more sensitive to

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you know, relative to other things

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I don't know, just trying to make connections

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This is less sensitive

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It's all big and open

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It won't be able to notice things that are small

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or maybe that is not an appropriate analogy

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but one way to think about it

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it's kind of open up wider,

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or it's bigger than a right angle

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it's larger than 90 degrees

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larger than 90 degrees

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if you measure it

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you would have to rotate this ray more to

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get to this other ray

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than you would if you had right angles

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and definitively a lot more if they were acute angles.

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If I were to draw this with lines,

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which of the angles are obtuse and

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which are acute?

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Well the way I drawn them right over here,

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these two over here are acute

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are acute

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and then these over here are going to be

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obtuse

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so this one

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and this one

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these are both obtuse angles

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and I actually drew them up here as well.

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This one and this one are going to be

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obtuse

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so very simple idea

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if one line

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or if one ray is relative to the other one

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is straight up and down

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versus left to the right

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or is completely upright

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then we're talking about a right angle

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if they are closer to each other

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if you had to rotate them less

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you're talking about a acute angle

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if you had to rotate them more

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you are talking about an obtuse angle

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and I think if you look at them visually

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it's pretty easy to pick out