Prove: Double angles

Because our teacher made a test hard enough that no one in our class understood, he decided to give it to us as open-book homework. I really need help with some questions.

Prove:
1 - tan^2x = cos2x
sec^2x

In case anyone doesn't know what I mean, ^2 means squared.

Thanks to whoever can help
 
Nov 2008
1,458
646
France
Hi

You should try by your own if you want to improve

\(\displaystyle \frac{1-\tan^2x}{\sec^2x} = \frac{1}{\sec^2x}-\frac{\tan^2x}{\sec^2x} = \cos^2x - \sin^2x = \cos(2x)\)
 
I tried by myself for a couple hours, so I was kind of just wasting time. Thank you so much for helping me, I actually understand this one now