If a ⊂ b, then a ∩ b = a ∪ b. always sometimes or never

Sometimes. Proof:

Assume .

Let , so that and . Then of course , so .

Now let , so that *or* . Since , if then , so that . But if , then , so it's not always the case that , and therefore in general .

1. sometimes

2. never true

3. sometimes

step-by-step explanation:

these are pretty self explanatory if you know what supp right and com angles are