December 26th, 2013, 10:13 AM  #1 
Newbie Joined: Dec 2013 Posts: 1 Thanks: 0  Math problem
Hi I have some problem solving this. I know I should use Euler's formula but I get stuck here. http://puu.sh/5Zmxt.jpg How do I continue from here? And this one. http://puu.sh/5ZmPT.jpg Any idea how to solve this one? 
January 10th, 2014, 01:32 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 19,731 Thanks: 1809 
As sin(3x) = 3sin(x)  4sin³(x), sin³(x) = (sin(3x) + 3sin(x))/4, so sin³(x)cos(3x) = (2sin(3x)cos(3x) + 6sin(x)cos(3x))/8 = (sin(6x) + 3sin(4x)  3sin(2x))/8. The second problem is mistyped. Assuming it should be one gets Hence x = ? ± ?/6 + 2k?, where k is an integer. 

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