# write tan10x in terms of tan5x (?!)

• April 13th 2008, 06:28 PM
blair_alane
write tan10x in terms of tan5x (?!)
We are supposed to:

"write tan10x in terms of tan5x."

I'm stumped! I don't remember learning this!

Do you know the double angle formula for $\tan (2\theta )$:
$\tan (2\theta) = \frac{2 \tan \theta}{1 - \tan^{2} \theta}$
Here, imagine $\theta = 5x$