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December 3, 2016
Posted by **-** on Sunday, November 8, 2009 at 10:29am.

2sinxsiny = cos(x-y) - cos(x+y)

- advanced functions -
**drwls**, Sunday, November 8, 2009 at 10:59amRewrite the right side, using

cos (x + y) = cos x cos y - sin x sin y

cos (x - y) = cos x cos y + sin x sin y

You should be familiar with those two identities. - advanced functions -
**nando**, Wednesday, October 15, 2014 at 6:53pmkagr