Answer:

Explanation:
Given that:

Also,
is in first quadrant.
To find:

Solution:
Let us have a look at the cosine of twice the angle in terms of tangent of the angle.
Suppose, we are given the value of
, then the formula can be written as:

In terms of
, we can re-write the formula as:

is in first quadrant, but
can be in the second quadrant therefore, we have a negative value of our answer i.e.
.
Therefore, the answer is:
