June 20th, 2017, 03:44 PM  #1 
Newbie Joined: Jun 2017 From: San Jose Posts: 1 Thanks: 0  Trigonometry proof
Using Only the definition of the trigonometric functions in terms of exp(x): cotx= i(e^ix+e^ix) /(e^ixe^ix) Prove: (cotx  1)/(cotx + 1) = cos2x/(1 + sin2x) Last edited by skipjack; June 20th, 2017 at 09:41 PM. 
June 20th, 2017, 09:47 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 18,953 Thanks: 1599 
This is straightforward. Can you post your attempt?

June 21st, 2017, 04:51 AM  #3 
Math Team Joined: Jul 2013 From: काठमाडौं, नेपाल Posts: 878 Thanks: 60 Math Focus: सामान्य गणित 
Probably its: (cotx  1)/(cotx + 1) = cos2x/(1 +i sin2x) 

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