MathematicsClass 7Lines and Angles
Complementary and Supplementary Angles
Identifying pairs of angles whose measures sum up to 90 degrees or 180 degrees respectively.
Class 7 · MathematicsCBSE & ICSE SOF IMO
Definition
Complementary angles are two angles whose sum of measures is 90 degrees. Supplementary angles are two angles whose sum of measures is 180 degrees.
Key formula
Angle 1 + Angle 2 = 90 degrees (Complementary) or 180 degrees (Supplementary)
Worked examples
1
If an angle measures 40 degrees, its complementary angle measures 50 degrees because 40 + 50 = 90.
2
If an angle measures 110 degrees, its supplementary angle measures 70 degrees because 110 + 70 = 180.
3
Two angles measuring 45 degrees each are complementary because their sum is 90 degrees.
Common mistakes
- • Mixing up complementary (90 degrees) and supplementary (180 degrees) angle sums.
- • Assuming that complementary or supplementary angles must always be adjacent to each other.