Question #592c3

1 Answer
Dec 14, 2015

When the angle between them is between 90\deg and 270\deg

Explanation:

scalar product of two vectors is given by \vec{a}\dot\vec{b}=|a||b|cos\theta,where \theta is the angle between the two vectors. The modulus of vectors are always positive, so the only way the scalar product is negative would be if \cos \theta is negative, which is for (90, 270)\deg