Trigonometric Identities

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) [A, B, & A+B does not = pi/2]

sin(2A)

2sinAcosA

cos(2A)

cos²A-sin²A

2cos²A-1

1-2sin²A

tan2A

2tanA/(1-tan²A) [A does not equal pi/2 or pi/4]

sin²A+cos²A

1

Limit Trig. Functions

lim_x→0sinx/x=1

lim_x→0(1-cosx)/x=0

lim_x→0tanx/x=1

cosecant (csc)

reciprocal of sine

csc=1/sin

secant (sec)

reciprocal of cosine

sec=1/cos

cotangent (cot)

reciprocal of tangent

cot=1/tan

Reciprocal Identities

sin/cos=tan

cos/sin=cot

sin²+cos²=1

tan²+1=sec²

cot²+1=csc²

sin(A/2)

cos(A/2)

tan(A/2)

sin²A

cos²A

tan²A

Law of Cosines

*gamma = angle opposite to c

Law of Sines