(I). Addition Formula
➭ 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
(II). Trigonometry Angle sum C-D Formula-
➭ SinC+SinD = 2Sin(C+D/2) Cos(C-D/2)
➭ SinC-SinD = 2Cos(C+D/2) Sin(C-D/2)
➭ CosC+CosD = 2Cos(C+D/2) Cos(C-D/2)
➭ CosC-CosD = 2Sin(C+D/2) Sin(D-C/2)
➭ CosC-CosD = -2Sin(C+D/2) Sin(C-D/2)
(III). Conversions Formula
➛ 2SinACosB = Sin(A+B)+Sin(A-B)
➛ 2CosASinB = Sin(A+B)-Sin(A-B)
➛ 2CosACosB = Cos(A+B)+Cos(A-B)
➛ 2SinASinB = Cos(A-B)-Cos(A+B)
(IV). Two angle formula
➛ Sin2A = 2SinACosA
➛ Cos2A = Cos²A-Sin²A = 2Cos²-1 = 1-2Sin²A
➛ tan2A = 2tanA/1-tan²A
➛ Sin2A = 2tanA/1+tan²A
➛ Cos2A = 1-tan²A/1+tan²A
(V). Specific formula
➛ Sin(A+B)Sin(A-B) = Sin²A-Sin²B
= Cos²B-Cos²A
➛ Cos(A+B)Cos(A-B) = Cos²A-Sin²B = Cos²B-Sin²A
(VI). Three angle formula
➛ Sin3A = 3SinA-4Sin³A
➛ Cos3A = 4Cos³A-3CosA
➛ tan3A = 3tanA-tan³A/1-3tan²A
(VII). Important Identities:
(i). Sin²θ+Cos²θ = 1
➭ Sin²θ = 1-Cos²θ
➭ Cos²θ = 1-Sin²θ
(ii). 1+tan²θ = Sec²θ
➭ Sec²θ-tan²θ = 1
➭ tan²θ = Sec²θ-1
(iii). 1+Cot²θ = Cosec²θ
➭ Cosec²θ-Cot²θ = 1
➭ Cot²θ = Cosec²θ-1
