Two angles whose sum is 180° are called supplementary angles.

Quick Scoop

What does “two angles whose sum is 180°” mean?

When you take the measures of two angles and add them, and the result is 180°, those two angles are a special pair called supplementary angles.

Example: 70∘+110∘=180∘70^\circ +110^\circ =180^\circ 70∘+110∘=180∘, so 70° and 110° are supplementary.

Key facts (at a glance)

  • Two angles with sum 180° → supplementary angles.
  • They can be:
    • Adjacent (next to each other, forming a straight line).
* Not adjacent (separate, but still add to 180°).
  • Common example: a linear pair on a straight line, like 60° and 120°.

Tiny story to remember it

Imagine a straight line as a 180° “road”.
If two angle “friends” stand on that road and perfectly fill it with no gaps or overlaps, their measures must add to 180°, so they are supplementary.

Whenever you see 180° in angle sums, think “sup-ple-men-ta-ry.”

HTML mini-fact table

html

<table>
  <tr>
    <th>Angle pair description</th>
    <th>Sum</th>
    <th>What they are called</th>
  </tr>
  <tr>
    <td>Two angles whose sum is 180°</td>
    <td>180°</td>
    <td>Supplementary angles</td>
  </tr>
  <tr>
    <td>Two angles forming a straight line</td>
    <td>180°</td>
    <td>Linear pair (and also supplementary)</td>
  </tr>
  <tr>
    <td>Two angles whose sum is 90°</td>
    <td>90°</td>
    <td>Complementary angles</td>
  </tr>
</table>

TL;DR: Two angles whose sum is 180° are called supplementary angles.

Information gathered from public forums or data available on the internet and portrayed here.