Question 1058531
This looks fine.
You factored out an x^2.  I would have factored out a 2x^2 and had (1-cos 52) inside.  Either way, you get the same answer.  You had two equal lengths, so everything on the right was expressed in terms of 1 variable. 
c^2=a^2+a^2-2(a)(a)cos (52) is another way to look at it.