newton333 Posted February 10, 2013 Share Posted February 10, 2013 Link to comment Share on other sites More sharing options...
Crimson Sunbird Posted February 11, 2013 Share Posted February 11, 2013 [latex]\sin x+\sin y = 2\sin\frac{x+y}2\cos\frac{x-y}2=\pm2\sin\frac{x+y}2\sqrt{1-\sin^2\frac{x-y}2}[/latex]NB: [latex]\cos\frac{x-y}2=\color{red}\pm\color{black}\sqrt{1-\sin^2\frac{x-y}2}[/latex] as [latex]\cos\frac{x-y}2[/latex] can be negative (e.g. when [latex]x=270^{\circ},y=30^{\circ}[/latex]). 1 Link to comment Share on other sites More sharing options...
newton333 Posted February 11, 2013 Author Share Posted February 11, 2013 thank you Link to comment Share on other sites More sharing options...
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