A 129° angle is an obtuse angle: wider than a right angle (90°) but less than a straight line (180°). Its supplement is 51°, so a 129° angle and a 51° angle side by side make a straight line.
129° is 43/120 of a full circle, or 43π/60 radians. If you face north and turn 129° clockwise, you end up facing between ESE and SE (closest to southeast (SE)).
129° angle facts
| Angle type | Obtuse angle (between 90° and 180°) |
|---|---|
| Supplement (adds to 180°) | 51° |
| Explement (adds to 360°) | 231° |
| Radians | 43π/60 ≈ 2.251475 |
| Gradians | 143.3333 grad |
| Fraction of a turn | 43/120 (35.83%) |
| Degrees, minutes, seconds | 129° 0′ 0″ |
| Compass bearing | between ESE and SE (closest to southeast (SE)) |
Trigonometric values of 129°
| Function | Value |
|---|---|
| sin 129° | 0.777146 |
| cos 129° | −0.62932 |
| tan 129° | −1.234897 |
129° on a protractor
How to draw a 129° angle with a protractor
- Draw a straight line with a ruler. This is the first arm; mark the vertex at one end.
- Place the center mark of the protractor exactly on the vertex and line up the 0° baseline with your line.
- Find 129° on the row of numbers that reads 0° on your line (protractors have two rows running in opposite directions) and make a small dot at the edge.
- Remove the protractor and draw a line from the vertex through the dot. Mark the angle with an arc and label it 129°.
Drawing it a 129° angle without a protractor (rise and run method)
- 129° = 180° − 51°. Draw a straight line, pick a vertex on it, and build a 51° angle on one side as follows; the angle on the other side of the new line is 129°.
- Draw a straight baseline and measure 8.1 inches (about 8 1/8″) along it from the vertex.
- At that mark, draw a line straight up at 90° and measure exactly 10 inches up it.
- Join the top mark to the vertex. The angle at the vertex is 51°, because tan 51° ≈ 1.2349.
Where you see 129° angles
- The Earth turns 129° on its axis in about 8 h 36 min.
- Obtuse angles like 129° appear in reclining chair backs, open laptop screens, fan blades, and the corners of many-sided polygons.
Related angles
129° angle FAQ
What type of angle is 129°?
A 129° angle is an obtuse angle, because it is between 90° and 180°.
What is the supplement of 129°?
The supplement of 129° is 51°, because 129° + 51° = 180°. A 129° angle has no complement, because it is already larger than 90°.
How many radians is 129 degrees?
129° = 43π/60 radians ≈ 2.2515 rad. To convert degrees to radians, multiply by π/180: 129 × π/180 = 43π/60.
How do I measure a 129° angle on my screen?
Open the online protractor with 129° preset, or type 129 into its "Type an angle" box. You can then drag the arms onto your own lines to compare.
