Answer/Step-by-step explanation:
For ∆ABC and ∆DEF to be similar the following must be true:
1. ∠A ≅ ∠D
2. ∠B ≅ ∠E
3. ∠C ≅ ∠F
4. The ratio of the length of their corresponding sides must be equal and proportional.
That is:
If all these are true, then ∆ABC ~ ∆DEF, because the corresponding angles of two similar shapes are equal, while the ratio of their corresponding side lengths are equal.