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## #1 Re: Help Me ! » Proving an Idenity » 2005-12-14 15:28:45

How would you work it from here?

cos²5x - cos²x = (-sin4x)(sin6x)
(cos5x - cosx)(cos5x + cosx)

?

## #2 Re: Help Me ! » Proving an Idenity » 2005-12-14 14:52:01

Are there any "more basic" ways you whould attempt doing it.  Or without using that specific formula. IDK what I am asking. Maybe he didn't teach us that because its only a Pre-Cal class.

## #3 Re: Help Me ! » Proving an Idenity » 2005-12-14 14:22:21

Its funny he has never shown us that formula sinAsinB = 1/2(cos(A-B) - cos(A+B)). Is it a given?

## #4 Re: Help Me ! » Proving an Idenity » 2005-12-14 13:46:42

darn that is great. However he said it could be proven in 4-5 steps by only working the left side.... Not to be picky, but you wouldn't happen to know how do do it like that?

PS: (Sorry I am being picky, I have a test on this type of problem tomarow.)

Thanks so much for your help

## #5 Re: Help Me ! » Proving an Idenity » 2005-12-14 12:47:07

You can use the identities. The words he really used were varifying Trigonometric Idenities. "Proving" that one side equals the other side, or the working of one side to equal the other.

Hope that helped.