Explanation

Angle addition identities allow trig functions of sum or difference of angles.

Key identities:
sin(A + B) = sin(A)cos(B) + cos(A)sin(B)
cos(A + B) = cos(A)cos(B) − sin(A)sin(B)

Used to:

• Simplify expressions

• Find exact values

Quiz

1. What do angle addition identities involve?

2. Is sin(A + B) equal to sin(A) + sin(B)?

3. Which trig functions appear in these identities?

4. Are these identities always true?

5. What are they mainly used for?

Answer Key

1. Sum or difference of angles

2. No

3. Sine and cosine

4. Yes

5. Simplification