Give all radian solutions to The only place where i know where to begin is would i need to reduce the cos(7x) like until i get down to cos(2x)? so i could use the identity Can anyone help me get started on this beast?
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Remember the identity cos ( A-B) = cos A cos B + sin A sin B use it and we have cos 5x = 1/2 now you can complete the solution.
would i then use cos(5x) = cos(3x + 2x) is that the way to go? or would i use arccos? 5x = arccos(1/2)
Last edited by icelated; August 21st 2013 at 12:26 AM.
No as mentioned the identity is cos ( A-B) = cos A cos B + sin A sin B What we have is LHS = cos(7x)cos(2x) + sin(7x)sin(2x) = cos ( 7x - 2x ) = cos 5X thus we get cos 5x = 1/2
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