Trigonometric Identities.

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10-26-2008, 05:28 PM
Goldenboko

Trigonometric Identities.

Still trying to perfect these, I ain't too good at them yet.

How do I show that (1+cos#)(1-cos#)=sin^2#

I get to 1-cos^2#=sin^2#

But then I forget what to do :o
10-26-2008, 05:35 PM
qwertysaur

1-cos² = sin²
10-26-2008, 05:35 PM
Goldenboko

Seriously? I was hoping it was that easy! xD

I might be back for more help in a bit xD
10-26-2008, 06:01 PM
rubah

don't forget about sec^2=1 + tan^2!
10-26-2008, 06:04 PM
Yar

Okay, Boko. We get it. You're smart. :mad2:
10-26-2008, 06:09 PM
Goldenboko

If I was smart I wouldn't be asking for help Yar-Yars!
10-26-2008, 06:18 PM
qwertysaur

Quote:

Originally Posted by RubyLapiz

don't forget about sec^2=1 + tan^2!

Yeah, there are 5 that you absolutely have to memorize, but 4 of them are derivable from the first

sin² + cos² = 1

subtract sin² to get

cos² = 1 - sin²

subtract cos² to get

sin² = 1 - cos²

divide by sin² to get

1 + cot² = csc²

divide by cos² to get

1 + tan² = sec²

Just wait until you get the double angles, half angles and sum and difference equations mixed in there. You will have oh so much fun XD
10-26-2008, 07:14 PM
rubah

can you post the double angle and half angle formulas? I always forget them.
10-26-2008, 07:16 PM
Tavrobel

Double and Half Angles.
10-26-2008, 07:24 PM
Flying Mullet

This is why I like teachers who will let you have a cheat sheet with these identities on tests.
10-26-2008, 07:26 PM
Goldenboko

Quote:

Originally Posted by Flying Mullet

This is why I like teachers who will let you have a cheat sheet with these identities on tests.

My teacher wants me to memorize them. :(
10-26-2008, 07:30 PM
rubah

sadly, calculus teachers are not some of those teachers :'(

Double Angle Theorem (typed up from tav's link):
cos(2x )= cos²(x) - sin²(x)