identity proofs

• Jun 21st 2010, 06:59 PM
ink
identity proofs
I've been at this problem for almost an hour now, but nothing seems to work out right. Please help me get into the right footing on how to start it. (Doh)

cos 2A/1 + sin 2A = cot A - 1/cot A + 1
• Jun 21st 2010, 07:46 PM
Chris L T521
Quote:

Originally Posted by ink
I've been at this problem for almost an hour now, but nothing seems to work out right. Please help me get into the right footing on how to start it. (Doh)

cos 2A/1 + sin 2A = cot A - 1/cot A + 1

Start with $\dfrac{\cos(2A)}{1+\sin(2A)}$ and use the following facts:

- $\cos(2A)=\cos^2A-\sin^2A=(\cos A+\sin A)(\cos A-\sin A)$

- $\sin(2A)=2\sin A\cos A$

- $\sin^2A+\cos^2A=1$

Can you try to do the problem with this information?