cos2θ + sin2θ = 1,
1 + tan2θ = sec2θ,
cot2θ + 1 = cosec2θ,
sin (–θ) = –sin θ,
cos (–θ) = cos θ,
tan (–θ ) = –tan θ,
cos 2θ = cos2θ– sin2θ = 2 cos2θ– 1 = 1 – 2 sin2θ,
sin 2θ = 2 sin θ cos θ,
.
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) = ,
sin A + sin B = 2 sin (A + B) cos (A – B),
sin A – sin B = 2 sin (A – B) cos (A + B),
cos A + cos B = 2 cos (A + B) cos (A – B),
cos A – cos B = 2 sin (A + B) sin (B – A).
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