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anonymous
 5 years ago
Trig. Identities: Solve from one side only please to prove it
cos(3x) = 4 cos^3 x  3 cos x
anonymous
 5 years ago
Trig. Identities: Solve from one side only please to prove it cos(3x) = 4 cos^3 x  3 cos x

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dumbcow
 5 years ago
Best ResponseYou've already chosen the best response.0ok cos(3x) = cos(2x+x) using angle addition identity cos(2x+x) = cos(2x)cos(x)  sin(2x)sin(x) ... using double angle identities cos(2x) = 2cos(x)^2  1 sin(2x) = 2sin(x)cos(x) ... = (2cos(x)^2  1)*cos(x)  (2sin(x)cos(x))*sin(x) =2cos(x)^3  cos(x)  2cos(x)sin(x)^2 ... using trig identity sin(x)^2 = 1cos(x)^2 ... =2cos(x)^3cos(x)2cos(x)(1cos(x)^2) =4cos(x)^3  3cos(x)

dumbcow
 5 years ago
Best ResponseYou've already chosen the best response.0hope you can follow that

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0Yes, that is sooooo helpful! Thanks a bunch, I was really stuck!

dumbcow
 5 years ago
Best ResponseYou've already chosen the best response.0your welcome, its really just knowing which identies to use you to play around with it a little bit
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