The Householder reflection is
effective for intruducing zeros if there are ''many'' components to be
annihilated. If it is necessary to nullify only one component, sometimes
a couple of components, then usually the Givens method is used.
The Givens rotation is realized by an 
matrix
where 
and 
.
This matrix 
is evidently orthogonal. If 
and 
then
By setting
we get 
Example 2.2.1. Consider the annihilation of the
last component of the vector 
given in example 2.1.1 with Givens rotations.
Find the values of c and s:
Check
