Use factors to calculate limit

Question

I am stuck with this math problem. The question is:

Use factoring to calculate this limit

(see picture) https://i.stack.imgur.com/zc1re.jpg

The only thing I came up with was:

$$2b^2 + 2bs + s^2$$

Can anybody help me out.

Thanks so much!

Answer 1

Hint:

$$\lim_{s\to{b}}{s^4-b^4\over{s^2-b^2}}=\lim_{s\to{b}}{(s^2-b^2)(s^2+b^2)\over{s^2-b^2}}$$

This question involves factoring a difference of squares, which is governed by the following formula: $$a^2–b^2=(a-b)(a+b)$$