My Math Forum  

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

Trigonometry Trigonometry Math Forum


Thanks Tree1Thanks
  • 1 Post By v8archie
Reply
 
LinkBack Thread Tools Display Modes
December 3rd, 2016, 07:01 AM   #1
Newbie
 
Joined: Dec 2016
From: Ireland

Posts: 4
Thanks: 0

Question Trig Identities (please help!)

In the solution to a question, it says that 2sinAcosA.sinA is equal to 2cosA(1 - cos^2A).
How are they equal? I can't figure it out!

(Note that the question I am doing is to prove that cos3A = 4cos^3A - 3cosA.)

Last edited by skipjack; December 3rd, 2016 at 08:24 AM.
Aoife73 is offline  
 
December 3rd, 2016, 07:20 AM   #2
Math Team
 
Joined: Dec 2013
From: Colombia

Posts: 7,032
Thanks: 2342

Math Focus: Mainly analysis and algebra
$$2\sin{A}\, \cos{A}\, \sin{A} = 2 \cos{A}\, \sin{A}\, \sin{A} = 2 \cos{A}\, \sin^2{A} = 2\cos{A}\,(1-\cos^2{A})$$
Thanks from Aoife73

Last edited by v8archie; December 3rd, 2016 at 07:23 AM.
v8archie is online now  
Reply

  My Math Forum > High School Math Forum > Trigonometry

Tags
homework, identities, maths, trig, trigonometry



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
trig identities sara213 Trigonometry 14 August 5th, 2011 07:05 AM
Trig Identities Gokias Trigonometry 10 July 13th, 2011 03:14 PM
Trig Identities jelsier Algebra 2 May 25th, 2009 08:56 PM
Trig Identities kevv2692 Algebra 2 May 25th, 2009 08:29 PM
More trig identities jordanshaw Calculus 5 December 31st, 1969 04:00 PM





Copyright © 2017 My Math Forum. All rights reserved.