SOLUTION: Use sum/difference formulas to derive the formula for cos(3x) in terms of cosx. PLEASE HELP!

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Question 182274: Use sum/difference formulas to derive the formula for cos(3x) in terms of cosx. PLEASE HELP!
Answer by Edwin McCravy(20059)   (Show Source): You can put this solution on YOUR website!
Use sum/difference formulas to derive the formula for cos(3x) in terms of cosx. PLEASE HELP! 


cos(3x) 

= cos(2x+x) 

= cos(2x)cos(x) - sin(2x)sin(x)

= [2cos˛(x)-1]cos(x) - [2sin(x)cos(x)]sin(x) 

= 2cosł(x) - cos(x) - 2sin˛(x)cos(x) 

= 2cosł(x) - cos(x) - 2[1 - cos˛(x)]cos(x)

= 2cosł(x) - cos(x) - 2cos(x)[1 - cos˛(x)]

= 2cosł(x) - cos(x) - 2cos(x) + 2cosł(x)

= 4cosł(x) - 3cos(x)

Edwin
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