in this lesson we are going to measure angles using a protractor do you know what a protective this is what it looks like at the bottom we have a baseline with a center point in the middle a protractor usually has two measuring scales this one is on the outside and measures from the left zero degrees goes through ninety degrees all the way up to 180 degrees those confirms that a straight angle is 180 degrees which is something we did in a previous lesson the second measuring scale is on the inside and measures from the right it again starts at zero degrees goes through 90 degrees all the way up to 180 degrees please pause if you need more time here let's now use a protractor to measure angle ABC we begin by putting the protractor here in other words we line up the baseline with one arm of the angle and most important the center point of the protractor must lie exactly where the vertex or corner of the angle is we are now ready to measure the angle we do this from zero degrees on the left and measure around to the other arm of the angle the other arm lies at exactly 40 degrees we can therefore write that angle ABC equals 40 degrees and because it lies between 0 degrees and 90 degrees it is an acute angle please pause if you need to next we are asked to measure angle PQR first we need to line up the baseline with one arm of the angle and very important the center point must lie exactly on the vertex of the angle we again start at zero degrees which is on the right this time and measure around until we reach the other arm of the angle the other arm lies exactly halfway between 60 and 70 degrees we can therefore write that angle PQR equals 65 degrees [Music] this angle also lies between zero degrees and 90 degrees so again we have an acute angle please pause if you need to next we are asked to measure angle D EF we again begin by lining up the baseline with an arm of the angle and then we place the center point on the vertex of the angle then starting from zero degrees on the left we measure around until we reach the other arm the other arm lizard 90 degrees we can therefore write that angle de f equals 90 degrees angle D EF is therefore a right angle please pause if you need to next we are asked to measure angle X Y Zed step one is to line up the baseline with one arm of the angle and then we put the center point on the vertex of the angle we then start at zero degrees on the right and measure around until we reach the other arm the other arm lies at three lines beyond 120 degrees in other words at 123 degrees angle XYZ is therefore equal to 123 degrees and because the angle lives between 90 degrees and 180 degrees it is an obtuse angle please pause if you need to next we are asked to measure angle m and L I hope you recognize that reflex angle in other words bigger than 180 degrees but smaller than 360 degrees to measure a reflex angle you need to recall that a revolution is 360 degrees in other words if we take a full revolution at vertex n and we subtract this part which is an obtuse angle then we will get the size of the reflex angle less one to do it so to get the size of reflex angle MN L we begin with 360 degrees and we subtract and we need to subtract the yellow part let's measure it to do this we place the baseline on one arm of the yellow angle and put the center point on the vertex of the angle we then measure from zero degrees until we reach the other arm of the angle the size of the yellow angle is therefore 130 degrees this means we need to subtract 130 degrees from 360 degrees reflex angle MN owl is therefore 230 degrees please pause to check my working here is another reflex angle we are asked to measure what is step 1 because this is a reflex angle we need to subtract from 360 degrees and we need to subtract this yellow part let's go on to measure it to do this we line up the baseline on one arm of the yellow angle and place the center point on the vertex of the angle we then start at zero degrees and measure around until we reach the other arm the size of the yellow angle is therefore 40 degrees this means we need to subtract 40 degrees from 360 degrees reflex angle fgh is therefore 320 degrees this completes the lesson good luck with the test