Main content

## 4th grade

### Unit 11: Lesson 2

Angle introduction# Angle types review

CCSS.Math:

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 type | Angle size (in degrees) |
---|---|

Acute | Between 0, degrees and 90, degrees |

Right | Exactly 90, degrees |

Obtuse | Between 90, degrees and 180, degrees |

Straight | Exactly 180, 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.

*Want to learn more about angle types? Check out this video.*

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

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

## Want to join the conversation?

- is there any angle that could be greater than 180 degrees?(4 votes)
- no. After 180 degrees it starts bending backwards, and it would be a acute angle again. A circle equals 360 degrees though.(6 votes)

- Is there an angle over 720 degrees?(14 votes)
- Yes, angles can have any angle measure. But since there's only 360 degrees in a circle, we usually don't write angles any bigger than 360. A 720 degree angle is the same as a 360 degree angle.(1 vote)

- the last one confused me a little bit(12 votes)
- Yeah it was very confusing(3 votes)

- 9+9 =18 but you add a zero

to 18 90+90 = 180(9 votes)- so true and right DeAndre.(3 votes)

- Is a straight angle a 180 degree angle(6 votes)
- yes because 180 degree angle is straight like a straight angle(7 votes)

- hi am a new person for khan academy(8 votes)
- How is this "Right". Saying that everything around me is ATLEAST Right, Obtuse or strait? How and why? And if you go on drawing right, acute and obtuse angles then they don't let you make one how ever you want on the dots?(0 votes)
- How am I supposed to know what angle to make if it dosen't even tell me(4 votes)
- It already said what angle you need to make, which is a straight angle (180 degrees).(5 votes)

- why isn't 0 degree an acute angle?(4 votes)
- Because zero degrees would be considered one degree or 360 degrees. IT is like if you count sheep, you don't start with zero, you start with one and keep going.(3 votes)

- i poop in the morning i poop in the day i poop when the feeling comes my way(4 votes)
- That is inappropriate for the subject and the mind bathroom words are for the bathroom.(1 vote)