two angles whose sum is 180 degrees

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

Quick Scoop

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

• If you have angle A and angle B, and A+B=180∘A+B=180^\circ A+B=180∘, then A and B are supplementary angles.

• For example, a 70∘70^\circ 70∘ angle and a 110∘110^\circ 110∘ angle are supplementary because 70∘+110∘=180∘70^\circ +110^\circ =180^\circ 70∘+110∘=180∘.

Key facts

• Name: supplementary angles.

• Condition: the measures of the two angles add up to exactly 180 degrees.

• They can be adjacent (forming a straight line) or separate, as long as their measures total 180 degrees.

• Angles that add to 90 degrees instead are called complementary angles, which is a different concept.

Mini example story

Imagine a straight road that makes a perfect straight line at a junction.
One side of the junction is a 120∘120^\circ 120∘ angle, and the other side is 60∘60^\circ 60∘.
Together they “complete” the straight line of 180 degrees, so those two angles are supplementary.

SEO-style extras

• Focus idea: “two angles whose sum is 180 degrees” = supplementary angles.

• Common textbook fill-in-the-blank: “If the sum of measures of two angles is 180°, then the angles are ___.” Correct answer: supplementary.

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

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