
What Is Reflection and Line Symmetry With Formula and Examples
FAQs on Reflection and Symmetry in Geometry
1. What is reflection in geometry?
Reflection in geometry is a transformation that flips a figure over a line to create a mirror image. The line used is called the line of reflection.
- Each point and its image are the same distance from the line of reflection.
- The original figure and reflected image are congruent.
- Orientation is reversed (like a mirror image).
2. What is symmetry in maths?
Symmetry in maths means that a figure can be divided into parts that are exactly the same in shape and size. A shape has line symmetry if it can be folded along a line so both halves match.
- The dividing line is called the line of symmetry.
- A figure may have one, multiple, or no lines of symmetry.
- Examples include squares, circles, and equilateral triangles.
3. How do you reflect a point across the x-axis?
To reflect a point across the x-axis, keep the x-coordinate the same and change the sign of the y-coordinate, using the rule (x, y) → (x, −y).
- Example: Reflect (3, 5).
- The reflected point is (3, −5).
4. How do you reflect a point across the y-axis?
To reflect a point across the y-axis, keep the y-coordinate the same and change the sign of the x-coordinate, using the rule (x, y) → (−x, y).
- Example: Reflect (−4, 2).
- The reflected point is (4, 2).
5. What is the formula for reflection across the line y = x?
The formula for reflection across the line y = x is (x, y) → (y, x). This means the coordinates swap places.
- Example: Reflect (2, 7).
- The image becomes (7, 2).
6. What is the difference between reflection and rotation?
The main difference is that reflection flips a figure over a line, while rotation turns a figure around a fixed point.
- Reflection reverses orientation (mirror image).
- Rotation preserves orientation.
- Both are examples of rigid transformations because size and shape remain unchanged.
7. How many lines of symmetry does a square have?
A square has 4 lines of symmetry. These include:
- Two lines through the midpoints of opposite sides (vertical and horizontal).
- Two diagonal lines joining opposite vertices.
8. What is a line of symmetry?
A line of symmetry is a line that divides a shape into two identical mirror-image halves. If folded along this line, both halves match exactly.
- Also called an axis of symmetry.
- Some shapes have multiple lines, while others have none.
- A circle has infinitely many lines of symmetry.
9. Can a circle have reflection symmetry?
Yes, a circle has infinitely many lines of reflection symmetry. Any line passing through the center of the circle divides it into two equal mirror-image halves.
- Every diameter is a line of symmetry.
- This makes the circle highly symmetric compared to polygons.
10. What are common mistakes when reflecting points on a graph?
A common mistake when reflecting points is changing the wrong coordinate or not reversing the sign correctly. Key reminders include:
- Across x-axis: use (x, y) → (x, −y).
- Across y-axis: use (x, y) → (−x, y).
- Across y = x: use (x, y) → (y, x).
- Do not change both coordinates unless required.

































