Use the Sum-To-Product Formulas to Select the Sum or Difference $$\cos ( 5 \phi + 2 \pi ) + \cos 5 \phi$$

question 33

Multiple Choice

Use the sum-to-product formulas to select the sum or difference as a product.​ $$\cos ( 5 \phi + 2 \pi ) + \cos 5 \phi$$ ​

• A)​ \(- 2 \cos 5 \phi \cos \pi\)
• B)​ \(- 2 \cos 5 \pi\)
• C) \(2 \cos ( 5 \phi + \pi ) \cos \pi\)
• D)​ \(2 \cos ( \phi + \pi ) \cos \pi\)
• E)​ \(2 \cos ( 5 \phi + \pi )\)

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