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 2 years 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)
 2 years 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)

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pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0I've been at it for so long! I cant get it :(

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0We have only learnt compound angles, by the way

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

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1Or sum to product identities. Do any of these sound familiar.

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0Is it the cos(90x) kind of thing?

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1um, not really. Here, let me post a link.

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0Thanks Ill read it!

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0nope....never learnt those :s

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

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0Alright I really appreciate it

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0I found a note that our teacher wrote on the board! I dont get it though... he wrote

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

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0ignore the caps they are the same letter

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

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1Okay, Do you know the double angle formula?

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

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1Are you following what i mean here?

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

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1cosine of x is sine of (90x) right?

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1okay. so =sin(x+y) =sinxcosy+sinycosx =sinx sin(90y)+siny sin(90x)

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

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0one sec for the original question?

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0oh no! you are right it sin(xy)!!!!!!!

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1Ok, that makes more sense now.

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1Give me another minute to type this up.

zordoloom
 2 years ago
Best ResponseYou've already chosen the best response.1ok let me know if you can see it.

pottersheep
 2 years ago
Best ResponseYou've already chosen the best response.0I can see it! Im following through fine so far. Thank you so much
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