If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:4:05

Measuring angles using a protractor 2

CCSS.Math:

Video transcript

this is a video for the measuring angles module because clearly at the time that I'm doing this video there is no video for the measuring angles module this is a pretty neat module this was made by Omar Rizvan someone of our are amazing high school interns that we had this past summer in the summer of 2011 and what it really is is it makes you measure angles and he made this really cool protractor tool here so that you actually used this protractor to measure the angles there and so the trick here is you would actually measure the way you would measure any any angle using an actual physical protractor you'd want to put the center of the protractor right at the vertex of where the two lines intersect you can kind of view it as the vertex of the angle and then you'd want to rotate it so that preferably this edge this edge at zero degrees is that one of is that one of these is it one of these sides so let's do it so that this edge right over here is is right along this line so let me rotate it so then I'm going to rotate a little bit further that looks maybe maybe one more that's too far so that looks about right and then if you if you look at it this way you can see that the angle and I don't have my pen tool here I'm just using my regular web browser if you look at the angle here you see that the other line goes to 130 degrees so this angle that's what that we need to measure here is 130 degrees assuming you can read sideways so that is 130 degrees let me check my answer very good I got it right it would be embarrassing if I didn't let's do the next question I'll do a couple of examples like this so once again let us put the center of the protractor right at the vertex right over there and let's get this zero degree side to be on one of the sides so that this angle will kind of be within the protractor so let me rotate it this way and this really is pretty cool what Omar did with this module so let's see let's do it see one more time that's too far so that looks about right and then you can see that the angle right over here it is if we look at where the other line points to it is 40 degrees it is 40 degrees check answer very good let's do another one this is fun all right so let's get our protractor right over there you don't always have to do in that same order you could rotate it first so that the zero degrees is all you want to do is you want to rotate the zero degrees to one of the sides but so that the angle is still within the protractor so let's rotate it around so if you did it like that so you don't always have to do it in that same order although I think it's easier to rotate it when you have the center of the protractor at the vertex of the angle so we have to rotate it a little bit more so this is zero degrees is this line and then we as we go further and further up I guess since this is on the side looks like this other line gets us to 150 degrees and hopefully you're noticing that the higher to the degrees the more open this angle is and so this one right over here is 150 degrees and so let's do that 150 let's do one more now let me show you what not to do so what not to do is so you could put the you could put the center right over there and you might say okay let me put let me make the zero go right over on this side right over here so if you did that if you did that notice your angle would not be within the protractor so you won't be able to measure it and what you're attempting to do is measure this outer angle over here which is an angle but that's not the angle that this question is asking us to measure this little arc over here is telling us that that's the angle that we need to measure so that arc has to be within the protractor so let's rotate this protractor a little bit more I overdid it and so this looks like this is zero degrees and then this right over here is 60 degrees 60 degrees we got that one right - so hopefully that that helps you with this module that it's kind of kind of fun