Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

This forum is in permanent archive mode. Our new active community can be found here.

Pre-calc Proofs

edited September 2008
I don't need reasons, just the steps.

Cos2x=(1-tan^2x/1+tan^2x)

• edited September 2008
Here, have it in LaTeX
If you can't get it to a format you can read, your loss
Also, I've taken the double-angle identity for granted; I'd hope you'd remember that one by now.

\begin{align*}
\frac{1-\tan^2x}{1+\tan^2x} &= \frac{1-\sin^2x/\cos^2x}{1+\sin^2x/\cos^2x} \\
&= \frac{\cos^2x-\sin^2x}{\cos^2x+\sin^2x} \\
&= \cos^2x-\sin^2x \\
&= \cos2x \\
\end{align*}
Post edited by lackofcheese on
• No. How do you think you will learn if you ask others to make your homework?
• Whether or not he learns isn't really our problem. More to the point, it's not something we can enforce. If I hadn't told him, he'd google for the answer and find it in no time at all.
At least this way he'll learn some LaTeX I hope.
• That answer was so helpful =p. And don't worry, I've spent at least 30 minutes on this. I've tried to learn. Thanks though, I go learn latex to do this.
• Whether or not he learns isn't really our problem.
You once had a very different opinion.
• edited September 2008
Heh; I probably did, but cynicism creeps in oh so quickly.
It would probably be funny if you had a specific post of mine to show me.

Also, I guess it depends on one's mood at the time.
Post edited by lackofcheese on
• I've made some Excel that works for one problem; it was pretty easy but I can't be bothered making it do 10 at once / sequentially. However, of course, I won't give it to you.