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Formulae Sheet

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Arkansas State University Campus Querétaro

Formulae sheet - Trigonometric identities


The use of this formulae sheet is subject to the authorization of your instructor.

Other trigonometric functions: Addition identities:


sin θ cos θ
tan θ = cos θ cot θ = sin(x ± y) = sin(x) cos(y) ± cos(x) sin(y)
sin θ
1 1 cos(x ± y) = cos(x) cos(y) ∓ sin(x) sin(y)
sec θ = cos θ csc θ = tan x ± tan y
sin θ tan(x ± y) =
Periodicity identities: 1 ∓ tan x tan y

sin(x + 2π) = sin x cos(x + 2π) = cos x Double angle identities:


sec(x + 2π) = sec x csc(x + 2π) = csc x
sin(2x) = 2 sin x cos x
tan(x + π) = tan x cot(x + π) = cot x
cos(2x) = cos2 x − sin2 x
Cofunction identities: = 1 − 2 sin2 x
π 
sin − x = cos x = 2 cos2 x − 1
 2π 
cos − x = sin x Half angle identities:
 2π 
tan − x = cot x 1h i
2 sin2 x = 1 − cos(2x)
2
Pythagorean identities: 1h i
cos2 x = 1 + cos(2x)
sin2 x + cos2 x = 1 2
1 + tan2 x = sec2 x Law of sines
1 + cot2 x = csc2 x
sin α sin β sin γ
Parity identities: = =
a b c
Even Odd
Law of cosines
cos(−x) = cos(x) sin(−x) = − sin(x)
sec(−x) = sec(x) csc(−x) = − csc(x) a2 = b2 + c2 − 2bc cos α
tan(−x) = − tan(x) b2 = a2 + c2 − 2ac cos β
cot(−x) = − cot(x) c2 = a2 + b2 − 2ab cos γ

Figure 1: Definitions for the sides and angles appearing on the laws of sines and cosines

Source: Dennis G. Zill, “Calculus. Early Transcendentals”, 4th edition, McGrawHill.

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