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 July 16th, 2019, 10:29 PM #1 Newbie   Joined: Jul 2019 From: Italy Posts: 3 Thanks: 0 Trignometry Solve If tanA = 4/5 then (1-cosA)/(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 right-angled 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
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Quote:
 Originally Posted by Veera Pronto If tanA = 4/5 then (1-cosA)/(1+cosA) = ? ---------------------------------------------- Thank you. Understood well. The answer choices are (a) 1/2 (b) 1/8 (c) 1/16 (d) 1/4 So none matches.
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^2-a^2)/2bc with tanA = 4/5 then (1-cosA)/(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
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 Originally Posted by skeeter If $\sin{A} = \dfrac{4}{5}$, then choice (d) works ...
Or if tan(A)= 4/3 (which is equivalent if A is an acute angle).

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