Welcome to our community

Be a part of something great, join today!

Trigonometry trig fix


Well-known member
MHB Math Helper
Feb 5, 2012
srirahulan's question titled "trig fix" from Math Help Forum,

Prove that, \[\frac{1+\tan^{2}(\frac{\pi}{4}-A)}{1-\tan^{2}(\frac{\pi}{4}-A)}=\cos 2A\]
Hi srirahulan,

Consider the left hand side of the equation.



&=&\frac{1}{\cos 2(\frac{\pi}{4}-A)}\\

&=&\frac{1}{\cos (\frac{\pi}{2}-2A)}\\

&=&\frac{1}{\sin 2A}\\


\[\therefore \frac{1+\tan^{2}(\frac{\pi}{4}-A)}{1-\tan^{2}(\frac{\pi}{4}-A)} = \csc 2A\]

So I think there is either a mistake in the question or a typo on your part. :)