Trigonometry Hand Rule

Select an angle

√n 2 = ...

The Hand Rule Mnemonic

A simple way to remember standard trig values without a calculator.

For Sine, curl the finger of the angle you want, then count the fingers remaining towards the Thumb.

√n / 2

Click on any finger ($0^\circ$ to $90^\circ$).

Count all fingers on the Thumb side.

Place that count under the square root and divide by 2.

Learn the mnemonic in 15 seconds

This trick works because standard values for $\sin$ are $\sqrt{0}/2, \sqrt{1}/2, \sqrt{2}/2, \sqrt{3}/2, \sqrt{4}/2$!