Explanation:
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. It
has applications in both pure mathematics and applied
mathematics, where it is essential in many branches of science and technology.
http://en.wikipedia.org/wiki/Trigonometry
Complementary angle identities
Two angles whose sum is π/2 radians (90 degrees) are complementary. In the diagram,
the angles at vertices A and B are complementary, so we can exchange a and b
and change θ to π/2 − θ, obtaining:
(Our solved example in
mathguru.com uses this concept).
http://en.wikipedia.org/wiki/Proofs_of_trigonometric_identities
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