Section+6.4

Product-To-Sum And Sum-To-Product Identities I. Product-to-Sum Identities

1. cosAcosB = 1/2(cos(A + B) + cos(A - B)

2. sinAsinB = 1/2(cos(A - B) - cos(A + B)

3. sinAcosB = 1/2(sin(A + B) + sin(A - B))

II. Sum-to-Product Identities

4. sinA + sinB = 2sin(A+B/2)cos(A-B/2)

5. sinA - sinB = 2sin(A-B/2)cos(A+B/2)

6. cosA + cosB = 2cos(A+B/2)cos(A-B/2)

7. cosA - cosB = -2sin(A+B/2)sin(A-B/2)

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