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 = (A^2 + B^2 + 2ABCos theta)^(1/2)#
where #theta# is the angle between A and B when they are drawn tail to tail.

This is the law of cosines.