determine. the magnitude. of thr resultant V=v1+v2
By the law of cosines, if the angle between a and b is θ,
|a+b|^2 = |a|^2 + |b|^2 - 2|a||b|cos(180-θ)
So, |a+b|^2 = |a|^2 + |b|^2 + 2a•b
|a+b|^2 = |a|^2 + |b|^2 - 2|a||b|cos(180-θ)
So, |a+b|^2 = |a|^2 + |b|^2 + 2a•b