The angle which forms a straight line is called the 180-degree angle. In geometry, we will be introduced to different types of angles, such as acute angle, obtuse angle, right angle, straight angle, reflex angle and full rotation. The angle which measures 180 degrees is named the straight angle. The other angles are given here:

- Acute angle: The angle which is more than 0° and less than 90°
- Right angle: The angle which is equal to 90°
- Obtuse angle: The angle which is more than 90° but less than 180°
- Reflex angle: The angle which is more than 180°
- Full rotation angle: The angle equal to 360°

## How to Find 180-Degree Angle?

To measure any angle we can directly use a protractor or a compass. Here are the steps to find a 180° angle, given in a plain sheet.

- Draw a straight line which will be the arm of angle.
- Put a dot at one end of the line. This dot denotes the vertex of the angle
- Now place the center of the protractor above the dot or vertex and match the baseline of the protractor along with the arm of the angle.
- Mark the angle 180 degrees with a dot.
- Now join this dot to the vertex of the angle, which forms the second arm of the angle.

Hence, we get a straight angle.

### How to Draw a 180-Degree Angle Using a Compass?

To draw the straight angle using compass follow the below steps.

- First, draw a straight line using a ruler or scale and name it as XY.
- Now mark a point O in anywhere between X and Y.
- With O as a center point, draw an arc of any radius using a compass, from the left of point O to the right of O.
- This arc cuts the straight line at point P and Q.
- Hence, the angle POQ is the required 180 degree.

**Check: **To check if the angle is 180 degree or not, you can use a protractor by keeping the center of the protractor at the top of point O and measuring the angle POQ.

Also, read: Lines And Angles

### Table of Angles

As per the definition of different angles present in geometry, here is a brief description for each angle. Suppose θ is any angle, then;

Acute angle | 0° < θ < 90° |

Right angle | θ = 90° |

Obtuse angle | 90° < θ < 180° |

Straight angle | θ = 180° |

Reflex angle | 180° < θ < 360° |

Full rotation | θ = 360° |

## Solved Examples

**Q.1: If a straight angle is divided into two parts, and one angle measures 60 degree, then find the other angle.**

Solution: Let the unknown angle is x

Given, another angle = 60°

We know that;

Straight angle = 180°

Therefore,

x+60 = 180

x = 180 – 60

x = 120°

Hence, the other angle measures equal to 120°.

**Q.2: Two angles are supplementary. If one angle is equal to 45 degrees, find the other angle.**

Solution: Given, two angles are supplementary, thus the sum of the two angles forms a 180-degree angle.

Now given one angle is 45 degrees.

Let the other angle is x.

Thus,

45 + x = 180 (Supplementary angles adds up to 180 degrees)

x = 180 – 45 = 135 degrees

**Q.3: If two angles are equal to each other and also supplementary, then find the angles.**

Solution: Given, two angles are equal. Let the angles be x.

Also, given two angles are supplementary, therefore,

x+x = 180°

2x = 180°

x = 180/2

x = 90°

Therefore, both angles are 90° each.