2.1 derivative & tangent line

Question 1

What needs to be acknowledged for instantaneous velocity of a function s(t)?

Answer 1

That s’(t)=v(t)

Question 2

When is a function not differentiable?

Answer 2

When:
1. slope from the left ≠ slope from the right
2. there is a vertical tangent
3. the function is not continuous (no value means no slope at that value)