View Full Version : Hi 100 points to him who has brains and skillz
Forrest
04-20-2002, 09:36 PM
Hi guys,
Long time no post. I used to post as a guy named "Beldaran" but my account got totally messed up and I couldn't log in anymore, and it wouldn't send me my password. So I quit waiting for some one to fix it and I just re-registered. Oh well.
Anyways, I have a really hard extra credit math question that I'm stuck on. Can anyone figure this out? (Glenn? Come one, big guy I need you on this one...)
Prove the following identity:
cos(a-b) * cos(a+b) = cos^2a - sin^2b
where "a" and b" are meant as angles "alpha" and "beta" and, even though its not important, are in radians.
I've so far reduced it down to:
cos^2a*cos^2b - sin^2a*sin^2b = cos^2a - sin^2b
I'm pretty much stuck. Whoever gets it figured out should get some major brain points.
PS - Nice to see you folks again.:)
Cyclone
04-20-2002, 09:46 PM
Hi Beldaran, maybe WL will be able to help you with your old account. LEt's hope so. :thumbsup:
And I have both good news and bad news. The good news is that I've seen this before.
The bad news is that I was never that skilled with sines, cosines, and the like. :shrug:
Glenn? :)
Cyclone
Forrest
04-20-2002, 09:50 PM
Hi nice to see you again Cyclone.
Yeah, its a tuffy. I've been staring at it long enough to where I know I'm just in a rut and won't get anywhere. I'm going to go do something else.
I would, of course, still like to hear form anyone who may have insight on it.
DarkDragon
04-20-2002, 10:08 PM
Yes, no problem.
cos(a-b) * cos(a+b) = cos(a)^2 - sin(b)^2
(cos(a)cos(b)+sin(a)sin(b))*(cos(a)cos(b)-sin(a)sin(b)) = cos(a)^2 - sin(b)^2
cos(a)^2 * cos(b)^2 - sin(a)^2 * sin(b)^2 = cos(a)^2 - sin(b)^2
Since sin^2 + cos^2 = 1,
cos(a)^2 * (1-sin(b)^2) - (1 - cos(a)^2)sin(b)^2 = cos(a)^2 - sin(b)^2
cos(a)^2 - cos(a)^2 * sin(b)^2 - sin(b)^2 + sin(b)^2 * cos(a)^2 = cos(a)^2 - sin(b)^2
cos(a)^2 - sin(b)^2 = cos(a)^2 - sin(b)^2
Forrest
04-20-2002, 10:25 PM
Damn it! I knew I was overlooking one tiny little thing. I always do that. All I had to do was realize cos^2 = 1-sin^2
Thanks DarkDragon. You're the man of the hour by far.:)
Dechipher
04-20-2002, 10:28 PM
HEy belderan!!! Long time no see...
Forrest
04-20-2002, 10:29 PM
'sup decipher?
How's life treating you? Did I miss anything really juicy while I was away?
PS- I'm digging the "Hyrule Night" style set:thumbsup:
Tygore
04-20-2002, 11:11 PM
Oh, you're beldaran?
Is your first name really Forrest?
Are you my dad?
GameQueen
04-20-2002, 11:34 PM
oh, that's who you are!
forget my question in your other topic.
inori
04-20-2002, 11:36 PM
BELDARAN! Where the heck have you been?!?!?
You've gotta PM an admin ASAP so you can have your name back! And then you've got to promise never to leave again! :D
Dechipher
04-20-2002, 11:36 PM
too late, lol i already got it. DIIIE!!!!
Forrest
04-21-2002, 12:28 AM
Originally posted by Tygore
Oh, you're beldaran?
Is your first name really Forrest?
Are you my dad?
lol, yes my first name really is Forrest....and I'm not anyone's dad...yet.;)
I missed you folks. Nice to see you again, Inori. I'll get right on that pm so I can have a custom avatar again, although I'm digging on Albert.:)
Drunken Tiger
04-21-2002, 12:37 AM
Wussup Beldaran!!
havent seen you in a long time!!
Glad your back!!;)
Beldaran
04-21-2002, 01:20 AM
Hey looks as though I have the old account back. Thank you, admins. ;)
Rainman
04-21-2002, 11:53 AM
Wow, that was weird seeing Albert Einstein ask us a math question. :eek:
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions Inc. All rights reserved.