Example 1
Find the complement of 54°.
- Complementary angles add up to 90°.
- Subtract 54° from 90°.
- 90° - 54° = 36°.
Answer: 36°
📗 Class 7 maths · session 5 of 12 · 60 minutes · 🎁 free with an account
Lines and angles
Welcome to HQ, cadet! Captain Calc needs your help to solve line and angle mysteries today.
🤖 Written with Google's Gemini AI. A second AI solved all 55 questions without seeing the answers, and both agree. One of our teachers has not read it yet, so if something looks wrong, please tell us.
A complete lesson · 60 minutes
Teach it, see it, practise it, all on this page.
Open this page with your learner and work down it, or press Teach this lesson to go through it one step at a time on a big screen. Every section has something to do.
- Warm-up3 min
- Warm-up games5 min
- Complementary and Supplementary Angles8 min
- Adjacent Angles and Linear Pairs7 min
- Vertically Opposite Angles7 min
- Parallel Lines and Transversal Angles7 min
- Captain Calc's Angle Detector6 min
- Vertically Opposite Mystery5 min
- Transversal Laser Grid6 min
- Quiz5 min
- Set the project1 min
By the end you can
- Find complementary and supplementary angles accurately
- Identify linear pairs and adjacent angles on a straight line
- Calculate vertically opposite angles when lines intersect
- Solve angle problems involving parallel lines and transversals
Before you start
- Basic angle types like acute, obtuse, and right angles
- Solving simple one-step linear equations
Have ready
- A ruler and a protractor
- A notebook and a pencil
Class 7 · CBSE, ICSE and state boards
Warm-up · think first
Two angles form a straight line. One angle is 70°. What is the other angle in degrees?
Show the answer
110°. Angles on a straight line add up to 180°, so 180° - 70° = 110°.
Teacher tip: Ask students what special shape a 180° angle creates.
🎮 Warm-up games · 5 quick games
Play with Captain Calc
Six minutes with Captain Calc. Vote, say why, then show the answer.
- Which angle pair does not belong with the others? (30° and 60° · 45° and 45° · 20° and 70° · 50° and 130°)
Answer: 50° and 130° does not belong. The first three pairs add up to 90° (complementary), but 50° and 130° add up to 180° (supplementary). - Would you rather find the complement of 38° or the supplement of 138°? (Complement of 38° · Supplement of 138°)
Answer: Both equal 52°! 90° - 38° = 52° and 180° - 138° = 52°. - Two acute angles are complementary. (Always · Sometimes · Never)
Answer: Always. Two acute angles are each less than 90°, and two acute angles can add up to 90°. - An angle is equal to its complement. What is the measure of this angle in degrees?
Answer: 45°. If an angle equals its complement, x + x = 90°, so 2x = 90° and x = 45°. - Where do you see parallel lines cut by a transversal in everyday life?
Answer: You can see them on railway tracks with cross sleepers, window grills, ladder steps, and zebra crossings on roads.
Part 1 of 4 · learn, see, practise
Complementary and Supplementary Angles
Two angles are complementary if their sum is 90°.
Two angles are supplementary if their sum is 180°.
Captain Calc calls complementary angles the Right-Angle Crew and supplementary angles the Straight-Line Squad!
Example 2
Find the supplement of 115°.
- Supplementary angles add up to 180°.
- Subtract 115° from 180°.
- 180° - 115° = 65°.
Answer: 65°
Practise it
Start with the warm-up and go as far as you can. The stretch questions are meant to be hard.
Warm-up
Warm-up
Core
Core
Stretch 🔥
Stretch 🔥
Answers (for the teacher)
- 65
- 110
- 42
- 45
- 30
- 100
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Unlocking the rest of this lesson gives you:
- Part 2: Adjacent Angles and Linear Pairs, with practice at three levels
- Part 3: Vertically Opposite Angles, with practice at three levels
- Part 4: Parallel Lines and Transversal Angles, with practice at three levels
- Class activity 1: Captain Calc's Angle Detector
- Class activity 2: Vertically Opposite Mystery
- Class activity 3: Transversal Laser Grid
- A 10-question quiz
- After-class project: City Grid Angle Map
- Homework and a printable practice sheet with answers
- Teach mode and the minute-by-minute teacher's plan
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FAQ
Lines and angles: questions
What is the main difference between complementary and supplementary angles?
Complementary angles add up to 90 degrees, forming a right angle. Supplementary angles add up to 180 degrees, forming a straight line.
Do linear pairs always form a straight line?
Yes, by definition, the non-common arms of a linear pair form a straight line, which means their sum is always 180 degrees.
Are alternate interior angles equal for any two lines?
No, alternate interior angles are equal only when the two lines cut by the transversal are parallel.
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