This document contains a summary of trigonometric identities and formulas. It lists identities for addition, periodicity, cofunctions, double angles, half angles, Pythagorean identities, parity, and the laws of sines and cosines. Definitions for the sides and angles in the laws of sines and cosines are also provided in Figure 1.
This document contains a summary of trigonometric identities and formulas. It lists identities for addition, periodicity, cofunctions, double angles, half angles, Pythagorean identities, parity, and the laws of sines and cosines. Definitions for the sides and angles in the laws of sines and cosines are also provided in Figure 1.
This document contains a summary of trigonometric identities and formulas. It lists identities for addition, periodicity, cofunctions, double angles, half angles, Pythagorean identities, parity, and the laws of sines and cosines. Definitions for the sides and angles in the laws of sines and cosines are also provided in Figure 1.
This document contains a summary of trigonometric identities and formulas. It lists identities for addition, periodicity, cofunctions, double angles, half angles, Pythagorean identities, parity, and the laws of sines and cosines. Definitions for the sides and angles in the laws of sines and cosines are also provided in Figure 1.
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.