4) Relations between Trigonometric Functions:
5) Trigonometric functions of special angles:
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6) sin ( A ±
B ) = sin A cos B ± cos A sin
B
cos ( A ±
B ) = cos A cos B
sin A sin B
tan ( A ±
B ) =
7) sin^{2}A  sin^{2}B = sin ( A + B ) sin (A  B )
cos^{2}A  cos^{2}B = sin ( A + B ) sin ( A  B)
cos^{2}A  sin^{2}B = cos (A + B ) cos ( A  B)

