Answer:
a) 
b)
c) 
Step-by-step explanation:
a) Let <u>a</u>=<2,1,-3>
The magnitude of <u>a</u> is 

The unit vector in the direction of a is

Using the relation
, we have

b) Let a=2i - 3j + 4k



Using the relation
, we have

c) Let us first find the sum of <1, 2, -3> and <2, 4, 1> to get:
<1+2, 2+4, -3+1>=<3, 6, -2>
Let a=<3, 6, -2>
The magnitude is


The unit vector in the direction of <u>a</u> is

Using the relation
, we have
