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Trigonometric Identities

Double Angle Identity-Cosine:	$cos 2\theta = cos ^2 \theta - sin ^2 \theta = 2cos ^2 \theta - 1$
Double Angle Identity-Sine:	$sin 2\theta = 2sin \theta cos \theta$
Sum and Difference of Angles Identity-Cosine:	$cos ( { a + b }) = cos a cos b - sin a sin b$
	$cos ( {a - b }) = cos a cos b + sin a sin b$
Sum and Difference of Angles Identity-Sine	$\sin { a \pm b } = \sin a \cos b \pm \cos a \sin b$
Pythagorean Property-Cotangent and Cosecant	$csc ^2 \theta = cot^2 \theta + 1$
Pythagorean Property-Sine and Cosine	$sin ^2 \theta + cos ^2 \theta = 1$
Pythagorean Property-Tangent and Secant	$1 + tan ^2 \theta = sec ^2 \theta$

keywords: trigonometric, sine, cosine, sin, cos, double angle, identities