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March 29th, 2010, 07:18 AM  #1 
Newbie Joined: Mar 2010 Posts: 1 Thanks: 0  Trig simplification
Hi guys, I've got a math issue regrding trig... I need to show that tan (4 arctan(1/5)) = 120/119 for a proof I'm doing. How would I go about doing/simplifying this? Thanks 
March 29th, 2010, 09:10 AM  #2 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Trig simplification
Hi there; just use the identity twice. That is, find tan 2x assuming you know that tan x = 1/5, then use that to find tan (2(2x)). 

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