Which expression is equivalent to StartFraction 1 Over sine (2 x) EndFraction minus StartFraction cosine (2 x) Over sine (2 x) EndFraction?

Whenever two chords of a circle intersect, they form two pairs of vertical angles and each are equal to half the sum of the intercepted arcs.

angle CEA = angle BED = .5 (176 + 82) = .5 * 258 =
129 degrees
angle AED + angle CEB = 360 -258 =
102 degrees
Vertical angles are equal so
angle AED = 51 degrees = angle CEB
Source:
http://www.1728.org/circangl.htm