Evaluate each of the following:

Firstly, tan = tan ……(i)

Also, coscoscos ……(ii)

From (i) and (ii),

becomes,

Now,

We know that, for any x R, represent an angle in whose tangent is x.

We know that, for any x [-1, 1], represent an angle in whose cosine is x.

Hence,

Therefore, Principal Value of is 0.