Sum-to-Product Identities

Question 1

What is sin(a) + sin(b)?

Answer 1

2 sin((a + b)/2) cos((a - b)/2)

Question 2

What is sin(a) - sin(b)?

Answer 2

2 cos((a + b)/2) sin((a - b)/2)

Question 3

What is cos(a) + cos(b)?

Answer 3

2 cos((a + b)/2) cos((a - b)/2)

Question 4

What is cos(a) - cos(b)?

Answer 4

-2 sin((a + b)/2) sin((a - b)/2)