Top 10 math mnemonics

Here is the E E E rule for signs of permutations:

Even number of Even cycles makes an Even permutation.

Yes, the sign is $(-1)^ {sum_{c textrm{ cycle}} (|c|-1) }$, but I remember it better with the triple E rule.

I remember the beginning digits of the square root of two by counting the number of letters in each of the following words, and the sentence describes the square root of two, too.

** I have a root of a two whose square is two. **

1 4 1 4 2 1 3 5 6 2 3

There are a few at Wikipedia:

I've always liked this one on the contraction mapping theorem (also from Wikipedia, though it's no longer on the page):

If $M$'s a complete metric space/(Non-empty) it's always the case/That if $f$'s a contraction/Then under its action/Exactly one point of $M$ stays in place.

In the absence of suitable mnemonics, I highly recommend Anki for memorising stuff in general.

Mnemonics are vital to teaching and learning mathematics. They are often unique as many are number-based, and as a mathematics teacher, they are quite powerful tools to help students, colleagues and ourselves the mathematical concepts.

Several studies have been performed on the effectiveness of their use, such as in Effects of Mnemonic and prior knowledge instructional strategies on students' achievement in Mathematics (Akinsola and Odeyemi, 2014), that concluded the most effective form of mnemonic in mathematics are ones that link prior knowledge with new concepts.

Also, as most formula use algebraic terms, these could be used as the first letters to make a sentence, or as a word, as a memory trigger.

There are many resources for mathematical mnemonics online,mostly are for elementary and high school students, such as the Education World website, which has 36 examples on this site, mostly for basic skills; and OnlineMath Learning.com, which includes some trigonometry and algebra. A basic visual mnemonic is included in a presentation for quaternions.

I remember the equality $$Gamma(frac{1}{2}) = pi^{frac{1}{2}}$$ by writing $$Gamma( frac{1}{2}= Pi^{frac{1}{2}} $$ or $$Gamma(^{frac{1}{2}}= Pi^{frac{1}{2}} $$