Congruence (Edexcel IGCSE Maths A) : Revision Note

Congruence

What is congruence?

  • Two shapes are congruent if they are identical in shape and size

    • One may be a reflectionrotation, or translation of the other

  • If one shape is an enlargement of the other, then they are not identical in size and so are not congruent

How do we prove that two shapes are congruent?

  • To show that two shapes are congruent you need to show that they are both the same shape and the same size

    • If a shape has been reflected, rotated or translated, then its image is congruent to it

  • Show that corresponding sides are the same length

  • Show that corresponding angles are the same size

  • You do not need to show that they are facing in the same direction

Examiner Tips and Tricks

  • Tracing paper can help in the exam if you are unsure whether two shapes are congruent

    • Trace over one shape and then see if it fits exactly on top of the other

    • Only do this if the image is drawn to scale

Worked Example

Write down the letters of the two shapes below which are congruent to A.

4-5-1-congruence-we-question

Shapes C and D are congruent to A

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Naomi C

Author: Naomi C

Expertise: Maths Content Creator

Naomi graduated from Durham University in 2007 with a Masters degree in Civil Engineering. She has taught Mathematics in the UK, Malaysia and Switzerland covering GCSE, IGCSE, A-Level and IB. She particularly enjoys applying Mathematics to real life and endeavours to bring creativity to the content she creates.

Dan Finlay

Reviewer: Dan Finlay

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Dan graduated from the University of Oxford with a First class degree in mathematics. As well as teaching maths for over 8 years, Dan has marked a range of exams for Edexcel, tutored students and taught A Level Accounting. Dan has a keen interest in statistics and probability and their real-life applications.

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