Ok, this is more a general question...There's a picture if that helps for me to explain my question .

This is the example in my text book. So i was reading through how the derive the formula1/ Find the perpendicular distance of the point P(4, 5, 6) and the

plane x + 2y - 2z = 0.

Now what i don't understand with this...n is the same vector as PM...

So the modulus of n should be the distance of PM. But then if thats the case, the formula doesn't make sense because it would be saying

and we need to know |x| to work out |x|...therefore the formula is pointless...

I know this mustn't be the case and its just me not understanding.

Any help please ?

Thanks