Trigonometric Identities.

[Goldenboko]

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

[qwertysaur]

1-cos² = sin²

[Goldenboko]

Seriously? I was hoping it was that easy! xD

I might be back for more help in a bit xD

[rubah]

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

[Yar]

Okay, Boko. We get it. You're smart. :mad2:

[Goldenboko]

If I was smart I wouldn't be asking for help Yar-Yars!

[qwertysaur]

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

[rubah]

can you post the double angle and half angle formulas? I always forget them.

[Tavrobel]

Double and Half Angles. (http://www.sosmath.com/trig/douangl/douangl.html)

[Flying Mullet]

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

[Goldenboko]

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. :(

[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)