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Zero Vector, Unit Vector, Coinitial Vectors, Collinear Vectors, Equal Vectors, Negative of a Vector (Free Vector)

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**Zero Vector:** A vector whose initial and terminal points coincide, is called a zero vector (or null vector), and denoted as `vec 0` . Zero vector can not be assigned a definite direction as it has zero magnitude. Or, alternatively otherwise, it may be regarded as having any direction. The vectors `vec ("AA") , vec (BB)` represent the zero vector,**Unit Vector:** A vector whose magnitude is unity (i.e., 1 unit) is called a unit vector. The unit vector in the direction of a given vector `vec a` is denoted by `hat a`.**Coinitial Vectors:** Two or more vectors having the same initial point are called coinitial vectors.**Collinear Vectors:** Two or more vectors are said to be collinear if they are parallel to the same line, irrespective of their magnitudes and directions.**Equal Vectors:** Two vectors are said to be equal, if they have the same magnitude and direction regardless of the positions of their initial points, and written as `vec a =vec b`.**Negative of a Vector:** A vector whose magnitude is the same as that of a given vector , but direction is opposite to that of it, is called negative of the given vector.

For example, vector `vec (BA)` is negative of the vector `vec (AB)` , and written as `vec (BA) = - vec (AB)`.**Remark:** The vectors defined above are such that any of them may be subject to its parallel displacement without changing its magnitude and direction. Such vectors are called free vectors.