Trigonometry - Ch.5 Identities

• cos(a+b) = cosAcosB - sinAsinB

• cos(a-b) = cosAcosB + sinAsinB

• sin(a+b) = sinAcosB + cosAsinB

• sin(a-b) = sinAcosB - cosAsinB

• tan(a+b) = tanA + tanB/1 - tanAtanB

• tan(a-b) = tanA - tanB/1 + tanAtanB

Double Angle Identities

• cos2a = cos²A - sin²A

  • = 2cos²A-1

  • = 1-2sin²A

• sin2a = 2sinAcosA

• tan2a = 2tanA/1-tan²A

Half Angle Identities

• cosA/2= + square root 1+cosA/2

• sinA/2= + square root 1-cosA/2

• tanA/2= + square root 1-cosA/1+cosA or sinA/1+cosA or 1-cosA/sinA