limits at infinity of trigs

• Mar 8th 2014, 05:28 AM
kingsolomonsgrave
limits at infinity of trigs
Attachment 30336

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?
• Mar 8th 2014, 05:39 AM
Plato
Re: limits at infinity of trigs
Quote:

Originally Posted by kingsolomonsgrave
Attachment 30336

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 $t=2x$.
• Mar 8th 2014, 06:15 AM
kingsolomonsgrave
Re: limits at infinity of trigs
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Thanks much!!!