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Question
Express the following as the sum or difference of sine or cosine:
`cos (7"A")/3 sin (5"A")/3`
Solution
`= 1/2 [2 cos (7"A")/3 sin (5"A")/3]` ...[Multiply and divide by 2]
`= 1/2 [sin ((7"A")/3 + (5"A")/3) - sin ((7"A")/3 - (5"A")/3)]`
`= 1/2 [sin (12"A")/3 - sin (7"A" - 5"A")/3]`
`= 1/2 [sin 4"A" - sin (2"A")/3]`
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