SOLUTION: Use the sum-to-product and product-to-sum identities to prove: sin 8θ-sin 10θ = cot 9θ(cos10θ-cos8θ)

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Question 1161416: Use the sum-to-product and product-to-sum identities to prove:
sin 8θ-sin 10θ = cot 9θ(cos10θ-cos8θ)
Answer by Edwin McCravy(20060)   (Show Source): You can put this solution on YOUR website!


We work with the left side only first:



Rewrite 8θ as 9θ-θ and 10θ as 9θ+θ











Now we work with the right side only:



Rewrite 8θ as 9θ-θ and 10θ as 9θ+θ

















Both sides work down the same expression.

Edwin
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