We all know that .
Here is a good technique to remember this:
Write down .
Put your left index finger on . Now put your left middle finger on . Then go the opposite direction (like playing the piano). This is the first term. Do the same for the other terms. Keep playing this (as if you were playing the piano).
This is how I remember .
Its like playing the piano. Let your index finger, your middle finger, and your crown finger (left hand) represent respectively. Tap your index finger, then tap your middle finger. Then do the opposite. Now tap your crown finger, then tap your index finger. Now do the opposite. Now tap your middle finger, then tap your crown finger. Now do the opposite. Keep "practicing" this.
So we have: P Q R
I've always found that proctoring an Intro Physics test just after mid-semester is rather fun. The students have hit the cross-product by then and during the exam they're pulling their tendons and writhing around in their seats trying to apply the right hand rule to figure out the direction.
(Okay, so what if I'm a sadist? )
Ok you have written down. Put your index finger (left hand) on and your middle finger on . Thats . Note that the middle finger is on which corresponds to . Now tap your middle finger on and your index finger on . That's .
So our first term is: . Keep doing this.