I have learnt in class about finding the moment of a force F about a point A using the formula
M = r × F
where r is the vector directed from A to the point of origin of F
A textbook problem requires me to find the moment of a force about an axis. I had a look at https://en.wikipedia.org/wiki/Bending_moment#Computing_the_moment_of_force and found another formula:
M = e · (r × F)
However, now I cannot understand what r to take in this formula. The problem in my textbook requires me to find the moment of a force of 276.85N directed from (8,-3,0) to (0,0,6) along an axis directed from (12,0,0) to (0,4,-6). The answer provided is 1000Nm.