Minimum Memorize in Math – Go by 1st Principle

Do not remember these:
$latex boxed {
cos 3A = 4cos^{3} A – 3cos A
}$

$latex boxed {displaystyle
int frac {dx}{sec x}
=
int
frac {1}{sec x}
frac {sec x + tan x}{sec x + tan x}dx
}&fg=aa0000
$

However, it helps, though, to remember:
“Nine Zulu Queens Rule China”
$latex boxed {
mathbb{N}subset mathbb{ Z }subset mathbb{ Q }subset mathbb{ R} subset mathbb{ C }
}&fg=00bb00&s=3
$

How Much Mathematics Should a Student Memorize?