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I really need help with this Trig identity please!(Grade 12!)
How do I prove that sinxsiny = 2cos([x+y]/2)sin([x+y]/2)
 one year ago
 one year ago
I really need help with this Trig identity please!(Grade 12!) How do I prove that sinxsiny = 2cos([x+y]/2)sin([x+y]/2)
 one year ago
 one year ago

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pottersheepBest ResponseYou've already chosen the best response.0
I've been at it for so long! I cant get it :(
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
We have only learnt compound angles, by the way
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
So there is an identity that's called co function identies, do you know them?
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
Or sum to product identities. Do any of these sound familiar.
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
Is it the cos(90x) kind of thing?
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
um, not really. Here, let me post a link.
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
http://www.sosmath.com/trig/Trig5/trig5/trig5.html
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
Thanks Ill read it!
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
nope....never learnt those :s
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
Give me like 510 minutes. This one is a little tricky. I'll try to keep you updated with the steps.
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
Alright I really appreciate it
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
I found a note that our teacher wrote on the board! I dont get it though... he wrote
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
sinx + siny = sin(a+b) = sinacosB + cosAsinB sin(ab) = sinAcosB  cosAsinB sin(a+B) + sin (a  b) = 2sinAcosB
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
ignore the caps they are the same letter
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
Then he wrote : let : a+b = x a  b = y 2a = x+y x = (x+y)/2
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
Okay, Do you know the double angle formula?
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
okay, so cos([x+y]/2)sin([x+y]/2). This equal sin(x+y)
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
Are you following what i mean here?
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
how about this. 2cosAsinA=sin2a. A=(x+y)/2
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
cosine of x is sine of (90x) right?
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
okay. so =sin(x+y) =sinxcosy+sinycosx =sinx sin(90y)+siny sin(90x)
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
I have a quick question, is it sin(x+y)/2 or sin(xy)/2?
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
one sec for the original question?
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
oh no! you are right it sin(xy)!!!!!!!
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
Ok, that makes more sense now.
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
Give me another minute to type this up.
 one year ago

zordoloomBest ResponseYou've already chosen the best response.1
ok let me know if you can see it.
 one year ago

pottersheepBest ResponseYou've already chosen the best response.0
I can see it! Im following through fine so far. Thank you so much
 one year ago
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