Similarity & Scale
📋 What it is
Similar shapes have the same angles and proportional sides — same shape, scaled bigger or smaller.
🗣️ Coach says
Similar shapes are the same shape at a different size — like a photo and its enlargement. The angles stay identical; the sides all grow (or shrink) by the same scale factor. Ratios are the key.
🧠 Memory hook
Similar = same angles, sides scaled by ONE factor. Double every side → it's still similar (just bigger).
😂 Giggle
What do you get when you cross a math teacher with a clock?
Arithme-tick!
😲 Whoa!
Mapmakers use similarity every day: a 1:100,000 map is a shape similar to the real land, shrunk by exactly that ratio.
✅ Quick check: A photo is enlarged so every side triples. Is the new photo similar to the old one?
Say your answer out loud first — then reveal.
Yes — same shape, every side scaled by the same factor (3), angles unchanged.
Similarity needs equal angles and one common scale factor for all sides.
🧪 Try it! (2 minutes)
Measure a small photo and its bigger print. Divide matching sides — you get the same scale factor.