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91Ó°ÊÓ

express each sum or difference as a product of sines and/or cosines

cos2Ï‘+cos4Ï‘

Short Answer

Expert verified

2cos3ϑcosϑ

Step by step solution

01

Step 1. Given information

cos2Ï‘+cos4Ï‘

02

Step 2. Solving using identity

We know that :

cosx+cosy=2cosx+y2cosx-y2

Using it :

cos2ϑ+cos4ϑ=2[cos2ϑ+4ϑ2cos4ϑ-2ϑ2]cos2ϑ+cos4ϑ=2[cos3ϑcosϑ]

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