Mathwords: Trig Identities

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Trig Identities

Identities involving trig functions are listed below.

sin² θ + cos² θ = 1

tan² θ + 1 = sec² θ

cot² θ + 1 = csc² θ

sin (–x) = –sin x

cos (–x) = cos x

tan (–x) = –tan x

csc (–x) = –csc x

sec (–x) = sec x

cot (–x) = –cot x

Cofunction Identities, radians	Cofunction Identities, degrees
	sin (90° – x) = cos x	cos (90° – x) = sin x
	tan (90° – x) = cot x	cot (90° – x) = tan x
	sec (90° – x) = csc x	csc (90° – x) = sec x

Periodicity Identities, radians		Periodicity Identities, degrees
sin (x + 2π) = sin x	csc (x + 2π) = csc x	sin (x + 360°) = sin x	csc (x + 360°) = csc x
cos (x + 2π) = cos x	sec (x + 2π) = sec x	cos (x + 360°) = cos x	sec (x + 360°) = sec x
tan (x + π) = tan x	cot (x + π) = cot x	tan (x + 180°) = tan x	cot (x + 180°) = cot x

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