A little push on this trig identity

  • Thread starter aisha
  • Start date
  • #1
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A little push on this trig identity plz

[tex] \tan^2(x)= \frac {1-\cos(2x)} {1+cos(2x)} [/tex]

I need a little push I know from my other post that [tex] \cos(2x)=\cos^2 (x) - \sin^2 (x) [/tex] (can someone explain why?)
 

Answers and Replies

  • #2
609
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what is your questioin? proving the tan identity or the cos one?
 
  • #3
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I have to make the left hand side equal the right hand side I dont think it matters if you use cos or tan which ever one is easier.
 
  • #4
It would be easier to work with the right side.
So it would be like:

[tex]\frac {1-\cos(2x)} {1+cos(2x)}[/tex]

[tex]\frac {1 - (1 - 2\sin^2x)}{1 + 2\cos^2x - 1}[/tex] Double angle identities

[tex]\frac{2\sin^2x}{2\cos^2x}[/tex] 2's cancel out

[tex]\tan^2x[/tex]
 
  • #5
584
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Thanks sooo much BLUE SODA Im not good with the double angle identity thanks again :smile:
 

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