Example 1 · level 1
Find the complement of 85° (in degrees).
Show solution
- Complement = 90° − 85° = 5°.
Answer: 5
CLASS 7 MATHS · LINES AND ANGLES
Complementary, supplementary and vertically opposite angles
Complementary angles add to 90°, supplementary angles (and a linear pair) add to 180°. Vertically opposite angles are equal.
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Worked examples
Example 2 · level 2
Two angles forming a linear pair are (4x − 4)° and (3x − 5)°. Find x.
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- 7x − 9 = 180
- 7x = 189
- x = 27. (Angles: 104° and 76°.)
Answer: 27
Example 3 · level 3
Two supplementary angles are in the ratio 2 : 4. Find the larger angle (in degrees).
Show solution
- 6x = 180 → x = 30.
- Angles: 60° and 120°.
- Larger = 120°.
Answer: 120