[再寄小读者之数学篇](2014-11-19 $\sin(x+y)=\sin x\cos y+\cos x\sin y$)

$$\bex \sin(x+y)=\sin x\cos y+\cos x\sin y. \eex$$ Ref. [Proof Without Words: Sine Sum Identity, The College Mathematics Journal].

[再寄小读者之数学篇](2014-11-19 $\sin(x+y)=\sin x\cos y+\cos x\sin y$)_第1张图片

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