Explanation

Similarity means two shapes have the same shape but not necessarily the same size.

Key points:

1. Corresponding angles are equal

2. Corresponding sides are proportional

3. Scale factor: ratio of corresponding side lengths

Notation: ΔABC ~ ΔDEF → ΔABC is similar to ΔDEF

Example: A triangle with sides 3, 4, 5 and another with sides 6, 8, 10 → triangles are similar (scale factor 2).