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anonymous
 one year ago
how do I prove cos (x+y)= cosxcosy  sinx siny
anonymous
 one year ago
how do I prove cos (x+y)= cosxcosy  sinx siny

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ParthKohli
 one year ago
Best ResponseYou've already chosen the best response.1There's, of course, a geometrical method to do this. Do you have anything else in your mind? Complex numbers? Derivatives?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0can you give the answer of proving the identity using the geometrical method??/

ParthKohli
 one year ago
Best ResponseYou've already chosen the best response.1I don't want to draw the picture again, so here it is: http://2000clicks.com/mathhelp/CosOfSumEqualsProductOfCosMinusProductOfSin1.gif

ParthKohli
 one year ago
Best ResponseYou've already chosen the best response.1\[\cos(x+y) = AP/AD\]\[\cos(x) = AB/AC\]\[\cos(y) = AC/AD\]\[\sin(x) = BC/AC\]\[\sin(y) = CD/AD\]
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