December 3rd, 2016, 07:18 AM  #1 
Newbie Joined: Dec 2016 From: Ireland Posts: 4 Thanks: 0  Trig identities
I'm a little confused as to how sin2A/cos2A is equal to (1+ 1/cos2A) Can anyone explain? 
December 3rd, 2016, 07:53 AM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,232 Thanks: 2411 Math Focus: Mainly analysis and algebra 
I think you have made an error in your terms because they are not equal for all A, but only when $\sin 2A = 1+\cos 2A$

December 3rd, 2016, 09:47 AM  #3 
Newbie Joined: Dec 2016 From: Ireland Posts: 4 Thanks: 0  Hm I may have worded it wrong I have attached the solution that is in my textbook and im just a bit confused as to how they made the jump from sinA over cosA to become (1 + 1 over cosA)

December 3rd, 2016, 11:06 AM  #4 
Global Moderator Joined: Dec 2006 Posts: 18,704 Thanks: 1529 
The sin2A/cos2A is not simply replaced with (1 + 1/cos2A). Instead, sin2A/cos2A as an expression added to sin2A is replaced with (1 + 1/con2A) as an expression that sin2A is multiplied by. It's like doing P + P/Q = P(1 + 1/Q), but with sin2A and cos2A instead of P and Q respectively. 
December 3rd, 2016, 11:33 AM  #5  
Newbie Joined: Dec 2016 From: Ireland Posts: 4 Thanks: 0  Quote:
Quote:
Last edited by skipjack; December 3rd, 2016 at 12:38 PM.  

Tags 
identities, trig, trigo, trigonometric 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Trig Identities  brian890  Trigonometry  4  November 11th, 2011 03:20 PM 
Trig Identities  Natalie89  Algebra  2  February 28th, 2011 09:00 AM 
trig identities  kfarnan  Algebra  11  September 17th, 2010 03:25 PM 
Trig Identities  aceofnapalms  Algebra  3  February 8th, 2010 06:44 PM 
Trig Identities  jelsier  Algebra  2  May 25th, 2009 07:56 PM 