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In this video, let's discuss how to measure angles.

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Now, over here you have a point.

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Imagine that this point over here right now, one complete revolution around this point is divided into

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three equal parts and each part we call a degree.

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So if you move from here and keep rotating your like this, like this, like this and keep doing till

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you get back to here, we say that you have moved 360 degrees.

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All right.

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Let's take this as our reference line and we move in this direction.

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All right.

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Now we keep moving till we reach over here.

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Now you can see that we have formed 90 degrees right here.

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You can see we have 90.

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So we have taken up 90 out of 360 degrees to reach still here.

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But this type of an angle is 90 degrees and we call a 90 degree angle as a right angle.

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But this is a very important concept in geometry.

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Now, let's move on now say you keep rotating, all right.

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From here, you keep rotating in this direction and you reach over here.

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Now you can see that you have reached 180 degrees with this type of an angle is a 180 degree angle.

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And we call such an angle as a straight angle.

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All right, now say you keep rotating and you reach over here to this angle is 270 degree, right?

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Because you can see that this is 270 over here and you keep rotating till you reach over here itself.

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And that type of an angle is called a complete angle or it's 360 degrees because we have divided one

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complete revolution into 360 equal parts.

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And that's how we measure an angle.

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So if you have an angle like this, you must remember in your school days you would use a protractor

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and you can measure how many degrees this angle over here is.

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So this could be 30 degrees or it could be any measure.

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All right, let's move on.

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Now we know how to measure an angle.

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We have learned what is right angles.

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We have learned what a straight angle is and what a complete angle is.

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Let's move on.

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Let's see what we mean with acute right obtuse and reflex angles.

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We already know what right angles.

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That's a 90 degree angle right now.

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Let's move on.

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What is an acute angle?

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Say you have this angle over here right now.

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Over here, you can see that if this area over here was at this point right, that would have given

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us a 90 degree angle.

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Right.

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So definitely this angle over here is less than 90 degrees.

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Right.

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So that type of an angle is what we call an acute angle.

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And acute angle is in between zero and ninety degrees.

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All right.

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Now we know what the right angle is.

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That's a 90 degree angle, right?

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That's what we call her.

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Right angle.

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And what is an obtuse angle.

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Say you have an angle over here.

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Over here.

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If this right over here was over here, then it would have been a 90 degree angle.

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Right.

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So this angle over here is definitely greater than 90 degrees.

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And that is what we call an obtuse angle.

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And obtuse angle is between 90 degrees and 180 degree.

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And remember, over here, 090 are not included.

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Similarly, over here, 90 and 180 are not included.

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Right.

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Because the sign over here is just less than so.

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X has to be in between zero and ninety four, the angle to be an acute angle and the angle has to be

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between 90 and 180 degrees or to be an obtuse angle.

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All right, let's move on.

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What is a reflex angle that reflects angle is an angle which is greater than 180 degrees, but it has

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to be greater than 180 degrees.

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Now in these cases, we have seen an acute angle, right angle and an abuse angle.

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At the same time, you also see that it reflects reflex angle is formed, right?

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This angle, this angle and this angle.

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You can see this is greater than 180 degrees.

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Let's take an example.

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Let this angle be thirty degrees.

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We know that one complete revolution is 360 degree right there.

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Therefore, this angle over here will be 360 minus 30, which is equal to three thirty degree.

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What about this case?

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We have ninety degrees over here.

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Therefore, this angle over here will be 360 minus ninety, which is equal to 270 degrees.

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What about this angle over here?

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We know that this is an obtuse angle.

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Let's take an example.

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Let it be a hundred and ten degrees.

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In that case, this angle over here will be 360, minus one hundred and ten, which is equal to 250

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degrees.

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What we have seen, what an acute angle is, what an right angle is, what an obtuse angle is and what

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it reflects angles.

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Remember, a reflex angle is greater than 180 degrees.