Find the principal value of each of the following:
Let 
.
Then, cos y = 
= –cos 
= cos 
= cos 
We know that the range of the principal value branch of 
is [0,
] and cos 
Therefore, the principal value of 
is 
.
4
Find the principal value of each of the following:
Let .
Then, cos y =
= –cos
= cos
= cos
We know that the range of the principal value branch of is [0,] and cos
Therefore, the principal value of is .