Explanation:
Trigonometry
Trigonometry (from Greek trigōnon "triangle" + metron "measure") is a
branch of mathematics that studies triangles and the relationships between their sides and the angles between
these sides. Trigonometry defines the trigonometric functions, which
describe those relationships and have applicability to cyclical phenomena, such
as waves.
http://en.wikipedia.org/wiki/Trigonometry
Symmetry
When the trigonometric functions are reflected from certain
angles, the result is often one of the other trigonometric functions. This
leads to the following identities:
Reflected in θ = 0

Reflected in θ = π / 4
(cofunction identities)

Reflected in θ = π / 2




(Our solved example in mathguru.com uses
this concept)
http://en.wikipedia.org/wiki/List_of_trigonometric_identities
The above
explanation is copied from Wikipedia, the free encyclopedia and is remixed as
allowed under the Creative
Commons Attribution ShareAlike 3.0 Unported License.
(Our solved example in mathguru.com also uses the below concept.
This is our own explanation, it is not taken from Wikipedia.)
TRIGNOMETRIC FORMULA USED
sin A + sin B = 2 sin () cos ()