# 4.1 Vector

(A) Definition of Vector and Vector Notation

1. Vector is a quantity that has both magnitude and direction.
2. Scalar is a quantity that has magnitude only.
3. A vector can be presented by a line segment with an arrow, known as a directed line segment.

(B) Equality of Two Vectors

1. Negative vector of  $\stackrel{\to }{AB}$ has the same magnitude as  $\stackrel{\to }{AB}$ but its direction is opposite to that of $\stackrel{\to }{AB}$ .

2. A zero vector is a vector whose magnitude is zero. It is denoted by $\underset{˜}{0}$ .

3. Two vectors are equal if both the vectors have the same magnitude and direction.