Question

how save formulas in my mind permanently

Answer 1

Well a good way to do is to write it down again and again.Writing things down on paper while saying it aloud helps us to remember things better.Also making a list of all of them and sticking it in places that you frequently visits also helps.
Good luck!:)

Answer 2

Read them thoroughly, but I would suggest you understand the formula, font just mug up them. Try to understand what each component if a formula suggests.