Answer:
A. { -20, -10, 20 }
Step-by-step explanation:
Given:
The function is given as:

Let us simplify the function.
First, we use the identity 

Next, we use the identity 

Now, the function can be rewritten as:

Now, the zeros are those values of
for which 
Now, for
, we must have either of the factors 0.


The factors
and
can have no zeros as the first one has imaginary roots and second one is always greater than 0 irrespective of the
values.
So, the possible set of zeros are { -20, 10, 20 }.