My Math Forum  

Go Back   My Math Forum > High School Math Forum > Trigonometry

Trigonometry Trigonometry Math Forum


Reply
 
LinkBack Thread Tools Display Modes
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.
Veera Pronto is offline  
 
July 17th, 2019, 03:48 AM   #2
Global Moderator
 
greg1313's Avatar
 
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?
greg1313 is offline  
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.
Veera Pronto is offline  
July 17th, 2019, 07:48 AM   #4
Math Team
 
skeeter's Avatar
 
Joined: Jul 2011
From: Texas

Posts: 3,002
Thanks: 1587

Quote:
Originally Posted by Veera Pronto View Post
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.
skeeter is online now  
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.
Veera Pronto is offline  
July 17th, 2019, 10:56 AM   #6
Global Moderator
 
Joined: Dec 2006

Posts: 20,921
Thanks: 2203

Quote:
Originally Posted by skeeter View Post
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).
skipjack is offline  
Reply

  My Math Forum > High School Math Forum > Trigonometry

Tags
solve, trignometry



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Trignometry Help Confused18 Trigonometry 7 July 23rd, 2014 07:37 AM
Trignometry: Angle of Depression suood Trigonometry 3 August 30th, 2013 10:24 AM
inverse trignometry abcd1122 Trigonometry 1 July 4th, 2013 11:50 AM
a formula without trignometry islam Algebra 8 December 15th, 2010 10:04 PM
Trignometry: Angle of Depression suood Elementary Math 3 December 31st, 1969 04:00 PM





Copyright © 2019 My Math Forum. All rights reserved.