use a double- angle identity to find the exact value
sin22.5^ocos22.5^o

- anonymous

use a double- angle identity to find the exact value
sin22.5^ocos22.5^o

- katieb

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- anonymous

why I am still at 19 fans, after spending the last 5 hours working my *** out?

- anonymous

if you help me with this i will become a fan

- anonymous

ok, one min

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## More answers

- anonymous

the double angle identities are as follows:
\[\cos (A - B) = (\cos A)(\cos B) + (\sin A)(\sin B) \]
\[\cos (A + B) = (\cos A)\cos B - (\sin A)\sin B \]
\[\sin (A + B) = (\sin A)(\cos B) + (\cos A)(\sin B) \]
\[\sin (A - B) = (\sin A)(\cos B) - (\cos A)(\sin B) \]
alright andy :) you can lead from here ^_^

- anonymous

hmm, am I mixing it all up with the double angle identities? those are the sin and cos indentities , hmm, please correct me if I'm wrong ^_^

- anonymous

double angle identities go like this, egzample:
sin(2x)=2sinxcosx

- nowhereman

That is just the above with setting A=B

- anonymous

no the identities are
sin2A=2sineAcosA
cos2A-cos^2A-sin^2A
=1-2sin^2A
=2cosA-1

- anonymous

or right lol , thank you, alright angoo, give it a try ^_^

- anonymous

ok I am bad at this, I guess I must have skipped school the day this stuff was tought

- anonymous

give it a try :)

- anonymous

yeah same here

- anonymous

nah, stary, you go ahead, I dont get this stuff yet

- anonymous

ask your beloved google lol

- anonymous

well, Google can give me examples, and explanations, and I can learn from them, but it would take too much time... so just go ahead and do it mimi

- anonymous

this is my new signature btw:
▓▒░╔ᴧᴨᴅᴙiᴜs╖░▒▓

- anonymous

LOL

- anonymous

alright LoveL , let me get this clear :
you want to find the answer of :
sin(22.5)cos(22.5)? or do you want to find the exact angle for sin(22.5)=? or cos(22.5)=? ^_^
lol, it's filled with mystery, but I like it :)

- nowhereman

I will show you, first of all: \[\sin (22.5^\circ)\cos(22.5^\circ) = \sin(\frac{180^\circ}{8})\cos(\frac{180^\circ}{8}) = \sin(\frac{π}{8})\cos(\frac π 8)\]

- anonymous

nvm, follow up with nowhereman ^_^ he'll lead you through.

- anonymous

so, loveinglife, do you feel happy today? because I do, but I could become even more happy if you gift me a fan =D
In that case, I will give you a fan too, so you become a lifesaver, and I become a superstar, a clear winwin =D

- anonymous

LOL, and you're still on it

- anonymous

@BecomeMyFan im your fan now. thank you for trying

- nowhereman

Then \[\sin(\frac π 8)\cos(\frac π 8) = \frac 1 2 \cdot \left(2\sin(\frac π 8)\cos(\frac π 8)\right)\] Thus by applying that double arc formula on the inner part (in reverse direction if you want) you get \[=\frac 1 2 \sin(2\frac π 8) = \frac 1 2\sin(\frac π 4) = \frac 1 4 \sqrt 2\]

- anonymous

Oh my god your awesome. thank you soo much you just saved my trig grade

- nowhereman

You're welcome :-D

- anonymous

love, are you in highschool?

- anonymous

or in college

- anonymous

?

- anonymous

because if you are doing this stuff in high school, I must have skipped ALOT of it

- anonymous

im saddly in college and i thought i was good in math till i got here

- anonymous

:)

- anonymous

why am I still a mear star?

- anonymous

I wanna be a superstar

- anonymous

it was supposed to rhyme

- anonymous

=D

- anonymous

sorry cant help you there but im done, but i will probably be back at some point

- anonymous

it is part of a poem I am writting about OpenStudy

- anonymous

=)

- anonymous

you write poems?

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