How can the law of cosines be used to find the magnitude of a resultant?

1 Answer
May 31, 2015

If we are to add vector A and B and if A and B be their magnitudes, then

If R is the resultant and R it's magnitude,

then R=(A2+B2+2ABcosθ)12
where θ is the angle between A and B when they are drawn tail to tail.

This is the law of cosines.