L069 · Allow 10–15 minutes for learners ready to move on. Answers are available after an attempt.
Similar triangles have corresponding sides 6 cm and 15 cm. A 9 cm side corresponds to what length?
Scale factor 15/6=2.5, so 22.5 cm.
Are triangles with side sets 3,4,5 and 6,8,11 similar? Explain.
No. Ratios 2,2,2.2 are not constant.
Lesson L069: Similarity and lengths
Objective: Use similarity to calculate missing lengths and justify scale factors.
60-minute structure: 0-7 Connect & Check; 7-14 Share; 14-25 Present/model; 25-44 Apply route choice/practice; 44-52 independent exam-style check; 52-60 Recall & Review, WWW/EBI and next step.
I selected the correct geometric fact, theorem, formula or transformation and used a clear diagram with appropriate labels and units.
I will name the fact or theorem, show the substitution or construction step and check whether the size, direction and units of the result are reasonable.
Stretch: Similar triangles have corresponding sides 6 cm and 15 cm. A 9 cm side corresponds to what length?
Deep challenge: Are triangles with side sets 3,4,5 and 6,8,11 similar? Explain.