July 16th, 2019, 10:29 PM  #1 
Newbie Joined: Jul 2019 From: Italy Posts: 3 Thanks: 0  Trignometry Solve
If tanA = 4/5 then (1cosA)/(1+cosA) = ? Last edited by Veera Pronto; July 16th, 2019 at 10:43 PM. 
July 17th, 2019, 03:48 AM  #2 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond 
If tanA = 4/5 then we have a rightangled triangle with opposite side 4, adjacent side 5 and hypotenuse √41. That means cosA = 5/√41. Can you now complete the problem?

July 17th, 2019, 07:29 AM  #3 
Newbie Joined: Jul 2019 From: Italy Posts: 3 Thanks: 0 
Thank you. Understood well. The answer choices are (a) 1/2 (b) 1/8 (c) 1/16 (d) 1/4 So none matches. 
July 17th, 2019, 07:48 AM  #4 
Math Team Joined: Jul 2011 From: Texas Posts: 3,002 Thanks: 1587  If $\sin{A} = \dfrac{4}{5}$, then choice (d) works ... might be a misprint.

July 17th, 2019, 08:17 AM  #5 
Newbie Joined: Jul 2019 From: Italy Posts: 3 Thanks: 0 
Yes this gives correct answer. With sinA = 4/5 Also if we use the equation: cosA = (b^2+c^2a^2)/2bc with tanA = 4/5 then (1cosA)/(1+cosA) = 0.231 which almost = 1/4 = 0.25 But that involves lengthy calculation. Anyhow. Many thanks. 
July 17th, 2019, 10:56 AM  #6 
Global Moderator Joined: Dec 2006 Posts: 20,921 Thanks: 2203  

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