Sal's old angle videos
Acute right and obtuse angles The difference between acute, obtuse and right angles
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- In this video, I really wanted to introduce
- you to some terminology for some basic angle types
- and terminology. I wanted to introduce you to are
- acute angles, right angles, and obtuse angles.
- I think when we go through these,
- it will be pretty self-explanatory.
- And an acute angle is an angle --
- let me just draw them first
- then you might,
- you might,
- it might start to make sense.
- So an acute angle
- will look something like that.
- I draw two rays
- coming from a common point.
- I could also --
- so the acute angle could be this angle right over here.
- I could also draw an acute angle;
- maybe an angle that is formed from an intersection of two lines,
- so this angle would be acute,
- and so will this angle.
- They're both acute angles.
- We are going to see acute angles as ones
- that are --
- that since I haven't defined right angles yet.
- They are narrower,
- so we are going to see that they are
- smaller than right angles.
- Right angles are when the rays
- or the lines are going, oh
- I guess, I don't want to use the word "right"
- in my definition.
- They are kind of
- if one is going horizontal
- then the other one will be going vertical.
- so let me draw with rays first
- so the right angle
- this one is going from the left to the right
- and the other ray is going from the bottom
- to the top
- this angle right over here
- is a right angle
- and I could label it like that
- but as a traditional angle
- but the general,
- the general convention for labeling right angles
- is to put a little,
- a kind of a half of a box over there.
- That tells me that this is a right angle
- or, that if this is going left to right
- this is going perfectly top to bottom
- that this is a no way kind of
- that this is a completely,
- I guess the best way to think about it
- why it's called right
- is that this ray is completely upright
- compared to this ray over here
- let me draw with some lines
- if I have one line like this
- and I have another line like that
- a right angle over here
- actually all of these would have to be
- right angles
- it would mean that this line
- is completely,
- if this line were the ground,
- this line is completely upright
- relative to this line over here.
- so either these,
- so that is what a right angle means
- so now that we defined right angle
- I can give you another definition for acute angle
- so an acute angle has a measure
- or it's smaller than a right angle
- so you learn about radients and degrees
- which are different ways to measure angles
- so you'll see that a right angle
- can be measured as 90 degrees
- this over here is less than 90 degrees
- so this is less than 90 degrees.
- and one way to conceptualize this is
- that this angle,
- it's opening is smaller
- it's more narrow,
- it's lines are,
- you would have to rotate one line
- less to get to the other line
- then you would over here.
- here, you would have to move
- all the way over there
- here you only have to move it a little bit
- so the acute angle is less than a right angle
- so you might imagine already
- what an obtuse angle is
- it is greater than a right angle
- so let me draw a couple of examples
- of obtuse angles
- so an obtuse angle might look like
- let me get it a little clearer
- might look like that
- if it was a right angle,
- then this line over here
- would be,
- would look something like that
- it would be completely upright
- relative to this, if this were the ground.
- but we don't see that
- this orange ray over here is actually
- opened out wider
- it's opened up wider
- so it is obtuse.
- it is obtuse
- so this kind of comes from the actual
- everyday meaning
- acute means very sharp or very sensitive
- obtuse means not very sharp or not very sensitive.
- you could imagine this looks like a sharp point
- or it's, it's not opening up much.
- so maybe it's more sensitive to
- you know, relative to other things
- I don't know, just trying to make connections
- This is less sensitive
- It's all big and open
- It won't be able to notice things that are small
- or maybe that is not an appropriate analogy
- but one way to think about it
- it's kind of open up wider,
- or it's bigger than a right angle
- it's larger than 90 degrees
- larger than 90 degrees
- if you measure it
- you would have to rotate this ray more to
- get to this other ray
- than you would if you had right angles
- and definitively a lot more if they were acute angles.
- If I were to draw this with lines,
- which of the angles are obtuse and
- which are acute?
- Well the way I drawn them right over here,
- these two over here are acute
- are acute
- and then these over here are going to be
- obtuse
- so this one
- and this one
- these are both obtuse angles
- and I actually drew them up here as well.
- This one and this one are going to be
- obtuse
- so very simple idea
- if one line
- or if one ray is relative to the other one
- is straight up and down
- versus left to the right
- or is completely upright
- then we're talking about a right angle
- if they are closer to each other
- if you had to rotate them less
- you're talking about a acute angle
- if you had to rotate them more
- you are talking about an obtuse angle
- and I think if you look at them visually
- it's pretty easy to pick out
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