pottersheep
Stuck on Trig identities! :( Help please~
How do I prove
cos(x+y)cosy + sin(x+y)siny = cosx??



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tanjung
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just to understanding the formula :
cosAcosB + sinAsinB = cos(AB)

pottersheep
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Yep I understand

pottersheep
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I cant get the answer still though

tanjung
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change A to (x+y) and B to y

pottersheep
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I got it! Ha, it was easier than I thought :)

tanjung
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yep, very easy :)

pottersheep
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You can have the medal :)

tanjung
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thanks, lol