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April 28, 2016
Posted by **Simon** on Sunday, November 8, 2009 at 11:16pm.

I can't find any identities that can help me with this. I'm really confused

- Math -
**drwls**, Monday, November 9, 2009 at 10:22am1 + tan^2 x= (cos^2 x+ sin^2 x)/cos^2 x = 1/cos^2 x

Therefore

=(1-tan^2x)/(1+tan^2x)= cos^2x - sin^2x

= cos 2x