# Thread: trigonometry compund angle formula

1. ## trigonometry compund angle formula

Prove that $sec^2 \theta + cosec^2 \theta \equiv 4cosec^2 2\theta$

Really not sure about using the compound angle formula. Thanks for any help

2. $\sec^2\theta+\csc^2\theta=\frac{1}{\cos^2\theta}+\ frac{1}{\sin^2\theta}=\frac{\sin^2\theta+\cos^2\th eta}{\sin^2\theta\cos^2\theta}=$

$=\frac{1}{\sin^2\theta\cos^2\theta}=\frac{4}{4\sin ^2\theta\cos^2\theta}=\frac{4}{\sin^22\theta}=4\cs c^22\theta$

3. ## Finding the values

Thanks, I managed to work out what to do in the end. Can anyone tell me what you would do to find $\theta$ ?

4. aaahh, you post this as a trigonometric equation? i thought it was an identity as as solved by red_dog, YOUR post is an identity . . . .