Here’s a cute little poem:

I wish I knew

The root of two.

O charmed was he

To know root three.

So we now strive

To find root five.

The beginning of each stanza is a mnemonic for the number mentioned in the following line.

√ 2 = 1.414

√ 3 = 1.732

√ 5 = 2.236

I found this in Twenty Years Before the Blackboard by Michael Stueben. Steuben sites the sources as Dictionary of Mnemonics, London 1972. He doesn’t give any other information such as author or editor.

**Update**: Additional verse from the comments.

It rhymes with heaven

The root of seven.

**Update**: Here’s Python code to validate the mnemonics above.

from math import sqrt def validate(line, num): digits = [str(len(w)) for w in line.split()] x = int("".join(digits)) / 1000 assert(x == round(sqrt(num),3)) validate("I wish I knew", 2) validate("O charmed was he", 3) validate("So we now strive", 5) validate("It rhymes with heaven", 7)

**Related post**: Numbers worth memorizing.

Lo:

The root of four.

(The above comment had three emojis to represent three 0s of precision. For some reason they aren’t displayed, but it also works as it is.)

sqrt(7) = 2.646 (assuming we’re rounding, not truncating)

“heaven” rhymes with “seven”.

Perhaps some other reader can use these two facts.

It rhymes with heaven

The root of seven

…and from http://www.eudesign.com/mnems/_mnframe.htm is also:

We need more logistics

( 2 . 4 4 9 ) to know the root of six

To make it rhyme how about

Or:

The root of four.

The square root of six

It bore some conflicts

The scared root of six

It fled from conflicts