Show that in triangle ABC

I had tried to change cos A = cos (180 - (B+C) ) = - cos (b+C) = - cos B cos C + sin B sin C then stuck

Thanks

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- September 13th 2010, 09:27 AMsongokutrigonometry proof
Show that in triangle ABC

I had tried to change cos A = cos (180 - (B+C) ) = - cos (b+C) = - cos B cos C + sin B sin C then stuck

Thanks - September 13th 2010, 10:03 AMmathaddict
- September 13th 2010, 06:14 PMsongoku
- September 14th 2010, 06:19 AMmathaddict
- September 15th 2010, 12:56 AMsongoku