It depends what you call a 'formula'. Some useful standard results are called formulae. For ex -> a2 - B2 = (a+b).(a-b). This is called factorise form (or formula) of a2 - b2. It depends on the circumstances of the question to use it or not.

Similarly, a4 + b4 = (a2+b2)^2 - 2a^2b^2

OR, it is also equals to (a2-b2)^2 + 2a^2b^2

Similarly, a4 + b4 = (a2+b2)^2 - 2a^2b^2

OR, it is also equals to (a2-b2)^2 + 2a^2b^2

- 0