Brainlag PlusScale factors between similar shapes, missing lengths, and how areas and volumes scale (Higher).
Same shape, any size
Two shapes are similar if one is an enlargement of the other: the angles are equal and every length is multiplied by the same scale factor k.
Find k from one pair of matching sides, then multiply (small to big) or divide (big to small).
- Triangle ABC ~ triangle DEF, AB = 4 cm, DE = 10 cm
- k = 10 ÷ 4 = 2.5
- BC = 6 cm, so EF = 6 × 2.5 = 15 cm
- DF = 20 cm, so AC = 20 ÷ 2.5 = 8 cm
A line drawn parallel to one side of a triangle cuts off a smaller similar triangle. Compare the whole side with the whole side: AD with AB, not AD with DB.
The rest of this lesson and its 8 practice questions are in Plus.
Screen 1 of 4, free to read.
- 8 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards