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Current time:0:00Total duration:3:25

CCSS.Math:

right what I have right in front of me is the Khan Academy measuring angles measuring angles exercise I have a small part of it in this screen right over here and it's a pretty cool exercise because it has this little virtual protractor that we can use to actually measure angles and I want to give credit to the the person who built this protractor because I think it's pretty neat Omar is one who is actually a high school intern made this made this pretty neat module and so in general when you want to measure an angle what you want to do is you want to put the center of your protractor at the center of where I should say at the vertex of the angle or you want to put the vertex of the angle at the center of the protractor and then what you want to do is either rotate the angle or rotate the protractor in this case we're going to rotate the protractor you want to rotate the protractor so that the zero angle or the kind of the zero mark is at one of the sides of the angle and the other side of the angle is within the protractor so let's try to do that so if maybe we could put if we want to do that this zero side should be at this side of the angle so let's rotate it let's rotate it that way let me just keep rotating it I could just keep it pressed that's better all right all right that looks about right so one side is at the zero mark and then my angle my other side or if this was a ray it points to looks like pretty close to the 20 degree mark so I will type that in off the screen you don't see that and that is the right answer and then we can get another angle so let's try to measure this one right over here so once again place the center of the protractor at the center at the vertex of our angle we can place the zero Degree the base of the protractor at this side of the angle so let's just rotate it a little bit maybe one more time that looks about right and the angle is now opening up let's see the other side is pointing to 110 degrees and so this is larger than 90 degrees it's also an obtuse angle the last one was an acute angle this is obtuse 110 degrees more than 90 degrees let me type it in I got the right answer let's do a couple more of these so once again put the center of the pro factor at the vertex of our angle and now I want to rotate it there we go and this looks like a roughly an 80 degree angle not quite if I be really precise it looks like it's maybe 81 or 82 degrees but I'll just go with 80 as my as my best guess I got the right answer let's do one more of these so once again vertex of my angle at the centre of my protractor and then I want to put one side of the angle at the zero degree or not and I want to show you there's two ways to do that you could do this you could do just this but this isn't too helpful because the angle is now outside the other side it sits outside of the protractor so you want the zero degrees on the side so the other side is within the protractor so let's keep rotating it there we go and then our other side opens up where you could say points 270 degrees so this is an acute angle right over here so it is 70 degrees so I'll let you that leave you with that or look I'm ready to move on the exercise tells me and and and and now we can start talking more things about angles now that we know how to measure them