Question 141309
It is a common misconception to think that every function must be expressed in terms of y and x. That is NOT so. You can use any 'variables' to represent unknowns. It doesn't have to be x and y, it doesn't even have to be letters. You would use symbols if you wanted to.

So D is not correct.
 
The given equation is the sum of two perfect squares. Sums of two squares cannot be factored. Completing the square is not appropriate for this one. 
To find the solutions, set k(w) to 0 and solve. a is the simplest way to do that. c would work too.

{{{0 = -w^2 + 4}}}
{{{-4 = -w^2}}}
{{{4 = w^2}}}
-+2 = w