Reach for the Star | GCSE Mathematics

L069: Similarity and lengths

Objective

Use similarity to calculate missing lengths and justify scale factors.

Calculator: Non-calculator core; calculator optional only for checking where labelled.

Visual model for Similarity and lengths
Points route: Connect 2 · Share 2 · Apply 6 · Review 3 · Stretch 2 · Deep Challenge 3. Record your score honestly after you have checked your answer.

Recall

Retrieve the key fact or method needed for similarity and lengths.

Core practice

Similar triangles have corresponding sides 6 cm and 15 cm. A 9 cm side corresponds to what length?

Reasoning

Are triangles with side sets 3,4,5 and 6,8,11 similar? Explain.

Exam-style

Solve an exam-style problem involving similarity and lengths. Show working, include a check and interpret your answer.

WWW / EBI

Recall & Review: feedback and extension integration

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.

What Went Well (WWW)

I selected the correct geometric fact, theorem, formula or transformation and used a clear diagram with appropriate labels and units.

Even Better If (EBI)

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 and deep challenge

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.