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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 and 90
RightExactly 90
ObtuseBetween 90 and 180
StraightExactly 180
ReflexBetween 180 and 360
CompleteExactly 360

Right angles

A right angle is a 90 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.
One ray extends to the right of the vertex. Another ray extends upward. A square at the vertex connects the rays to represent a perfect corner, or a right angle.

Straight angles

A straight angle is a 180 angle. A straight angle looks like a straight line. Below is an example of a straight angle.
A straight line with a half circle on top and at the center of the line to represent a straight angle.

Acute angles

An acute angle is an angle whose degree measure is less than 90. Below is an example of an acute angle.
A ray extends to the right of the vertex. Another ray extends to the right and upwards from the vertex. A curved line connects the rays to represent an angle, in this case an acute angle, which has a degree measure less than 90 degrees.
When we compare an acute angle to a right angle, we can see that an acute angle is less than 90.
The acute angle from above set inside a 90 degree angle, called a right angle. Comparing the angles, the acute angle has a smaller degree of measure than the right angle.

Obtuse angles

An obtuse angle is an angle whose degree measure is greater than 90 but less than 180. Below is an example of an obtuse angle.
A ray extends to the right of the vertex. Another ray extends up and to the left of the vertex. A curved line connects the rays to represent an angle, in this case an obtuse angle, which has a degree measure of greater than 90 degrees but less than 180 degrees.
When we compare an obtuse angle to a right angle, we can see that an obtuse angle is greater than 90.
The obtuse angle from above with a 90 degree angle, called right angle, set inside it. Comparing the angles, the obtuse angle has a greater degree of measure than the right angle.
When we compare an obtuse angle to a straight angle, we can see that an obtuse angle is less than 180.
The obtuse angle from above set on a straight angle, or straight line. Comparing the angles, the obtuse angle has a smaller degree of measure than the straight angle.
Want to learn more about angle types? Check out this video.

Reflex angles

A reflex angle is an angle whose degree measure is greater than 180 but less than 360. Below is an example of a reflex angle.
A ray extends to the right of the vertex. Another ray extends down and to the left of the vertex. A curved line connects the rays to represent an angle, in this case a reflex angle, which has a degree measure of greater than 180 degrees but less than 270 degrees.
When we compare a reflex angle to a straight angle, we can see that a reflex angle is greater than 180.
The reflex angle from above set on a straight angle, or straight line. Comparing the angles, the reflex angle has a larger degree of measure than the straight angle.

Complete angles

A complete angle is a 360 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.
A ray extends to the right of the vertex. Another ray also extends to the right of the vertex, exactly on top of the first ray. A curved line that forms a full circle connects the rays to represent an angle, in this case a complete angle, which has a degree measure of 360 degrees.

Practice set 1: Identify angles

Problem 1A
Is the following angle acute, right, obtuse, or straight?
A ray extends from the vertex towards between 3 and 4 o'clock. A second ray extends from the vertex towards 5 o'clock. An arc connects these two rays.
Choose 1 answer:

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

Practice set 2: Angles in diagrams and images

Problem 2A
What type of angle is the angle highlighted in green below?
Choose 1 answer:
The letter K. Inside the top angle of the letter K, a ray extends from the vertex towards 12 o'clock. A second ray extends from the vertex towards between 1 and 2 o'clock. An arc connects these two rays.

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

Practice set 3: Drawing angle types

Problem 3A
Drag the vertex of the angle to place the vertex at point A.
Drag another point on the angle to make one of the rays go through point B.
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.

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