Complementary, supplementary and vertically opposite angles: Class 7 practice
Complementary angles add to 90°, supplementary angles add to 180°, and vertically opposite angles are equal. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Angles
The idea behind complementary, supplementary and vertically opposite angles
Complementary angles add to 90°, supplementary angles add to 180°, and vertically opposite angles are equal. Angles on a straight line form a linear pair (180°).
Step-by-step method
- Identify the angle relationship.
- Write the equation (sum = 90° or 180°, or equal).
- Solve for the unknown.
Worked example 1 (Basic)
Find the complement and supplement of 56°.
- Complement 90 − 56 = 34°
- Supplement 180 − 56 = 124°
- Answer: 34° and 124°
Worked example 2 (Standard)
Two supplementary angles are in the ratio 2 : 1. Find them.
- 2x + x = 180 → x = 60
- Answer: 120° and 60°
Worked example 3 (Challenge)
Two vertically opposite angles are (3x + 21)° and (4x + 3)°. Find x and the angle.
- 3x + 21 = 4x + 3
- x = 18
- Angle = 75°
- Answer: x = 18, angle 75°
Common mistakes and misconceptions
- Mixing up 90° and 180°
- Assuming adjacent angles are equal
Practice questions
- (Basic) Find the complement and supplement of 68°.
- (Basic) Find the complement and supplement of 39°.
- (Standard) Two supplementary angles are in the ratio 4 : 1. Find them.
- (Standard) Two supplementary angles are in the ratio 5 : 1. Find them.
- (Challenge) Two vertically opposite angles are (4x + 7)° and (5x − 26)°. Find x and the angle.
- (Challenge) Two vertically opposite angles are (3x + 10)° and (4x − 25)°. Find x and the angle.
Answer key with full working
- Q1: Complement 90 − 68 = 22° → Supplement 180 − 68 = 112° → Answer: 22° and 112°
- Q2: Complement 90 − 39 = 51° → Supplement 180 − 39 = 141° → Answer: 51° and 141°
- Q3: 4x + x = 180 → x = 36 → Answer: 144° and 36°
- Q4: 5x + x = 180 → x = 30 → Answer: 150° and 30°
- Q5: 4x + 7 = 5x + -26 → x = 33 → Angle = 139° → Answer: x = 33, angle 139°
- Q6: 3x + 10 = 4x + -25 → x = 35 → Angle = 115° → Answer: x = 35, angle 115°
Syllabus note
This skill is listed under "Lines and Angles" for Class 7 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is complementary, supplementary and vertically opposite angles in?
"Lines and Angles", Class 7 Maths (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.