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Symmetry (Including Reflection and Rotation) — Revision Notes

ICSE · Class 8 · Mathematics

Symmetry (Including Reflection and Rotation) revision notes for ICSE Class 8 Mathematics: 4 topics in quick points.

47 questions30 flashcards5 formulas & key relations5 concepts

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Key Topics to Revise

1

1. Symmetry and Line of Symmetry

  • A plane figure has symmetry if folding it about a line makes the two parts match exactly.
  • The line about which the figure is symmetrical is called a line of symmetry, axis of symmetry, or mirror line.
  • If a figure is symmetrical, points on one side match points on the other side at equal distances from the mirror line.
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2. Symmetry in Common Figures

  • A line segment is symmetrical about its perpendicular bisector.
  • An angle with equal arms is symmetrical about its bisector.
  • An isosceles triangle is symmetrical about the bisector of the angle at the vertex.
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3. Reflection of a Point in Coordinate Axes and Origin

  • When a point is reflected in the x-axis, only the sign of the y-coordinate changes.
  • When a point is reflected in the y-axis, only the sign of the x-coordinate changes.
  • When a point is reflected in the origin, both x and y signs change.
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4. Rotation About the Origin

  • Rotation through 180° about the origin changes both signs of the coordinates.
  • Rotation through 90° anticlockwise and 90° clockwise have different coordinate rules.
  • A point rotated through 90° anticlockwise moves to a new position with coordinates based on the rule P'(-y, x).

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Full Notes

Key Concepts

A plane figure is symmetrical ifA line segment is symmetrical aboutA rectangle and a rhombus eachAny line passing through the centreWhen a point P(x

Frequently Asked Questions

What are the important topics in Symmetry (Including Reflection and Rotation) for ICSE Class 8 Mathematics?
Key topics in Symmetry (Including Reflection and Rotation) include Symmetry and Line of Symmetry, Symmetry in Common Figures, Reflection of a Point in Coordinate Axes and Origin, Rotation About the Origin. Study these first, then practise questions on each for Class 8 exams.
How should I revise Symmetry (Including Reflection and Rotation) for Class 8 exams?
Learn the core ideas first, then work through the 47 practice questions on Symmetry (Including Reflection and Rotation). Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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