**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.