1) If  then magnitude or length or norm or absolute value of is
2) A vector of unit magnitude is unit vector. If  is a vector then unit vector of  is denoted by  and         
3) Important unit vectors are , where , ,
4) The components of unit vectors of   are called the direction cosines of , denoted by  and
5) If , , , then  are called directional angles of the vectors  and
6) If  and  are the two points, then
7) If   and  then


8) If  and  is a scalar number, then.
9) In vector addition
            I.    
            II.   
            III.
            IV.  ,        is the additive identity in vector addition.
            V.    ,        is the inverse in vector addition.