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19 terms

Trigonometric Identities

http://www.purplemath.com/modules/idents.htm
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sin(A+B)
sinAcosB+cosAsinB
sin(A-B)
sinAcosB-cosAsinB
cos(A+B)
cosAcosB-sinAsinB
cos(A-B)
cosAcosB+sinAsinB
tan(A+B)
(tanA+tanB)/(1-tanAtanB)
tan(A-B)
(tanA-tanB)/(1+tanAtanB)
sin2A
2sinAcosA
cos2A (in terms of both sin and cos)
cos²A-sin²A
sin(A/2)
±√((1-cosA)/2)
cos(A/2)
±√((1+cosA)/2)
tan(A/2) (in terms of cos only)
±√((1-cosA)/(1+cosA))
tan(A/2) (rationalized)
(1-cosA)/sinA and sinA/(1+cosA)
sinA + sinB
2sin((A+B)/2)cos((A-B)/2)
sinA-sinB
2cos((A+B)/2)sin((A-B)/2)
cosA+cosB
2cos((A+B)/2)cos((A-B)/2)
cosA-cosB
-2sin((A+B)/2)sin((A-B)/2)
sinAcosB
(1/2)(sin(A+B)+sin(A-B))
cosAcosB
(1/2)(cos(X-Y)+cos(X+Y))
sinAsinB
(1/2)(cos(X-Y)-cos(X+Y))