MA26-04 Maths Coming soon
Congruent and similar shapes: finding unknown lengths
MA26-04
This lesson is coming soon.
In this lesson
Distinguish congruent shapes from similar shapes, identify truly corresponding sides in similar figures, and calculate an unknown length using the scale factor.
What it covers
- Definition: congruent means exactly the same shape AND size
- Definition: similar means the same shape, scaled (angles unchanged, sides in the same ratio)
- Identifying which sides truly correspond between two similar figures
- Calculating an unknown length in similar figures using ratio/scale factor
Key words
For: Edexcel IGCSE 4MA1, Cambridge IGCSE 0580, OCR GCSE J560
On the specification
| Board | Spec | Statement |
|---|---|---|
| Edexcel IGCSE 4MA1 | F4.2F | Understand congruence as meaning the same shape and size |
| Edexcel IGCSE 4MA1 | F4.2G | Understand that two or more polygons with the same shape and size are said to be congruent to each other |
| Edexcel IGCSE 4MA1 | F4.11A | Understand and use the geometrical properties that similar figures have corresponding lengths in the same ratio but corresponding angles remain unchanged |
| Cambridge IGCSE 0580 | C4.4 | Calculate lengths of similar shapes. |
| Cambridge IGCSE 0580 | E4.4 | Calculate lengths of similar shapes. |
| OCR GCSE J560 | 9.04a | Identify similar triangles. |
| OCR GCSE J560 | 9.04c | Compare lengths, areas and volumes using ratio notation and scale factors. |
For teachers
This GCSE Maths lesson teaches congruent and similar shapes: finding unknown lengths. By the end, students should be able to distinguish congruent shapes from similar shapes, identify truly corresponding sides in similar figures, and calculate an unknown length using the scale factor. It works through three worked examples and the mistakes examiners report.