Scale and maps
Lesson 6 of 9
Similar shapes
Objective. Use a scale factor to find missing lengths in similar shapes.
The key idea
Similar shapes have equal angles and lengths in the same ratio. Find the scale factor from a matching pair of sides, then apply it.
Worked example
Two similar triangles: sides 3 cm and 12 cm match. Another side is 5 cm. Its pair?
- 1Scale factor: 12 ÷ 3 = 4.
- 25 × 4 = 20.
Answer: 20 cm
Practice
Each question comes with a picture and a listen button. Try it first, then reveal the answer.
Common mistake. Adding a constant difference instead of multiplying by a scale factor.
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