I have a project problem that reads:
Sounds easy. But I can't find anything about the sum identity in my book. :( Can anyone enlighten me?Quote:
Show how to derive the sin(2x) from the sum identity using sin(x + x).
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I have a project problem that reads:
Sounds easy. But I can't find anything about the sum identity in my book. :( Can anyone enlighten me?Quote:
Show how to derive the sin(2x) from the sum identity using sin(x + x).
Okay. I fooled around with this:
Where do I go from there? Am I going the wrong way?Quote:
sin(x + x) = sin(x)cos(x) + cos(x)sin(x) = 2sin(x)cos(x)
Christ it's been awhile since I did these ones... :p
Do you have all the rules anywhere?
The rules? *scans his book* No one told me about rules? :eek:Quote:
Originally posted by rjlohan
Do you have all the rules anywhere?
I have a crap-load of formulas I keep trying, but I'm not getting anywhere.
I don't want an answer here. Just a clue to get me from A to B. ;)
The clue is that you need the basic identities first.
e.g - sin(x + y) = sin(x)cos(y) + sin(y)cos(x)
:p
Bah! I got that. :cool:
I'm here: 2sin(x)cos(x)
How can I make that eqal to sin(2x)?
When you substitute x for 45, they come out as equal, but that's too big of a jump. How can I prove those two are equal without pluging in a value?
Is there some identity I'm not seeing? :confused:
fook me!
The Double-Angle Formula states that:
I already have it solved. :rolleyes:Quote:
sin(2x) = 2sin(x)cos(x)
I can't believe I just wasted an hour on that when it's already a pre-established identity.
Thanks for your help, rj.
An hour?!?! Why would it take an hour? You should already know that sin(x+y)=sinxcosy+cosxsiny, and if you didnt you could refer to your book. Then it takes two seconds after that to say sin(x + x) = sin(x)cos(x) + cos(x)sin(x) = 2sin(x)cos(x)= sin(2x)
Why should I already know that? Because you do? And I already mentioned that I didn't see it in the book.Quote:
Originally posted by SilverSprite
An hour?!?! Why would it take an hour? You should already know that sin(x+y)=sinxcosy+cosxsiny, and if you didnt you could refer to your book. Then it takes two seconds after that to say sin(x + x) = sin(x)cos(x) + cos(x)sin(x) = 2sin(x)cos(x)= sin(2x)
Way to be an ass, though. :rolleyes:
SilverSprite screwed up on a math contest so he isn't in a very good mood. Let me apologize for him.
Yes, i guess i should apologize too. I CANT BELIEVE 9+5=11!!!! And what's even more stupid is a misadded so many times.
He's not the only one who screwed up...
891>976
!!!:mad: !!!
Kalk how can you make such an amateur mistake!
try (6a)/(3a)=3! (not 3 factorial, just 3 with an exclaimation mark)