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## Class 5

### Course: Class 5>Unit 9

Lesson 3: Angle types

# Angle types review

Review the following types of angles: acute, right, obtuse, and straight.  Identify and draw types of angles in some practice problems.

### Summary of angle sizes

Angle typeAngle size (in degrees)
AcuteBetween 0, degrees and 90, degrees
RightExactly 90, degrees
ObtuseBetween 90, degrees and 180, degrees
StraightExactly 180, degrees
ReflexBetween 180, degrees and 360, degrees
CompleteExactly 360, degrees

### Right angles

A right angle is a 90, degrees angle. A right angle is in the shape of a perfect corner, like the corner of a rectangular sheet of paper. Below is an example of a right angle.

### Straight angles

A straight angle is a 180, degrees angle. A straight angle looks like a straight line. Below is an example of a straight angle.

### Acute angles

An acute angle is an angle whose degree measure is less than 90, degrees. Below is an example of an acute angle.
When we compare an acute angle to a start color #11accd, start text, r, i, g, h, t, space, a, n, g, l, e, end text, end color #11accd, we can see that an acute angle is less than 90, degrees.

### Obtuse angles

An obtuse angle is an angle whose degree measure is greater than 90, degrees but less than 180, degrees. Below is an example of an obtuse angle.
When we compare an obtuse angle to a start color #11accd, start text, r, i, g, h, t, space, a, n, g, l, e, end text, end color #11accd, we can see that an obtuse angle is greater than 90, degrees.
When we compare an obtuse angle to a start color #1fab54, start text, s, t, r, a, i, g, h, t, space, a, n, g, l, e, end text, end color #1fab54, we can see that an obtuse angle is less than 180, degrees.

### Reflex angles

A reflex angle is an angle whose degree measure is greater than 180, degrees but less than 360, degrees. Below is an example of a reflex angle.
When we compare a reflex angle to a start color #7854ab, start text, s, t, r, a, i, g, h, t, space, a, n, g, l, e, end text, end color #7854ab, we can see that a reflex angle is greater than 180, degrees.

### Complete angles

A complete angle is a 360, degrees angle. A complete angle has both rays pointing the exact same direction. That is because we've turned a full circle from the first ray. Below is an example of a complete angle.

### Practice set 1: Identify angles

Problem 1A
• Current
Is the following angle acute, right, obtuse, or straight?

Want to try more problems like this? Check out this exercise.

### Practice set 2: Angles in diagrams and images

Problem 2A
• Current
What type of angle is the angle highlighted in green below?

Want to try more problems like this? Check out this exercise.

### Practice set 3: Drawing angle types

Problem 3A
• Current
Drag the vertex of the angle to place the vertex at point start text, A, end text.
Drag another point on the angle to make one of the rays go through point start text, B, end text.
Make the other ray go through one of the unlabeled black points to create a straight angle.
The arc symbol near the vertex indicates the angle being measured.

Want to try more problems like this? Check out this exercise.