Fold & Fly
Each corner of a square is a right angle. When a diagonal crease runs from one corner to the opposite corner, it halves that corner’s 90° opening. Each half is 45°. The conclusion depends on the square and the equal split, not simply on having any slanting crease.
Before you try
What happens when a crease splits a square corner into two equal openings?
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What happened?
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The game practises one idea at a time with simple drawn pictures. Check the same idea with real objects and your NCERT textbook (Chapter 2: Shapes and Angles, pages 23).
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Try these ideas
- Sketch the diagonal from corner to opposite corner.
- Find a crease perpendicular to a side.
- Turn the paper and identify the same angle again.
Why it works
Each corner of a square is a right angle. When a diagonal crease runs from one corner to the opposite corner, it halves that corner’s 90° opening. Each half is 45°. The conclusion depends on the square and the equal split, not simply on having any slanting crease.
A crease drawn across the midpoints of two opposite sides meets those sides at right angles. Another crease can meet it at a different opening. Follow the marked pair of lines before naming the angle; one busy fold pattern may contain several different openings.
Open a folded paper aeroplane gently and inspect its creases. You may find 45° and 90° angles, as well as other openings. Crease Sketcher isolates one fold at a time. The paper turns on the screen, but a rotation leaves the angle between its crease and edge unchanged.
Worked example: A diagonal halves a 90° square corner. How large is each new angle? The corner begins at 90°. The diagonal makes two equal parts. 90° ÷ 2 = 45° for each part.
Check your understanding
Question 1 of 2
Half of a right angle is…
Rotating the folded square changes the crease angle.
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Fold and mark · 8 minutes. Fold a paper square diagonally, open it and label the two 45° parts at a corner.
- Plane detective · 10 minutes. Open a paper aeroplane and use a tester to identify selected crease openings. Mark only the pair of lines being compared.