1. Two angles are complementary if their sum is:
- A90 deg
- B180 deg
- C360 deg
- D270 deg
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Answer: A) 90 deg
By definition, two angles are complementary when their measures add up to 90 deg.
Class 9 Pairs of Angles — practice questions with answers
Geometry — Lines and Angles · 5 sample questions from the school syllabus. Try each one, then open the answer and the worked solution.
2. Two lines intersect at a point. One angle is 72 deg. What is the measure of each angle adjacent to it?
- A216
- B108
- C98
- D118
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Answer: B) 108
Each adjacent angle forms a linear pair with 72 deg, so it equals 180 - 72 = 108 deg.
3. Two lines AB and CD intersect at O. If angle AOC = (5x) deg and angle BOD is vertically opposite to it and equals (3x + 40) deg, find x.
- A40
- B22
- C20
- D18
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Answer: C) 20
Vertically opposite angles are equal: 5x = 3x + 40, 2x = 40, x = 20.
4. Two angles are supplementary. If thrice the smaller angle equals the larger angle, find the smaller angle (in degrees).
- A45
- B90
- C49
- D41
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Answer: A) 45
Let smaller = x, larger = 3x. x + 3x = 180, 4x = 180, x = 45 deg.
5. An angle exceeds its complement by 10 deg. The supplement of this same angle exceeds the angle itself by how many degrees?
- A80
- B160
- C72
- D88
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Answer: A) 80
Let the angle be x. x = (90 - x) + 10, so 2x = 100, x = 50 deg. Supplement = 180 - 50 = 130. It exceeds the angle by 130 - 50 = 80 deg.
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