# Thread: limits at infinity of trigs

1. ## limits at infinity of trigs

how does [cos(4x)-1] become [1- 2sin^2x -1] = 2sin^2x ?

which really means cos(4x) becomes 1-sin^2x

which trig identity does this use?

2. ## Re: limits at infinity of trigs

Originally Posted by kingsolomonsgrave

how does [cos(4x)-1] become [1- 2sin^2x -1] = 2sin^2x ?

which really means cos(4x) becomes 1-sin^2x

which trig identity does this use?
$\cos(2t)=1-2\sin^2(t)$ let $t=2x$.

3. ## Re: limits at infinity of trigs

This forum is really quite amazing. As amazing as mathematics is, I think the people who love it and create it are equally inspiring.

I would bet, statistically speaking, that the level of generosity among mathematicians/math nerds (at least with respect to sharing mathematics) is much higher than that of the general population. Just look at this forum and others like it, or Khan academy and PatrickJMT (both of whom voluntarily post hundreds if not thousands of math videos on youtube for free)!

Thanks much!!!