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本刊1986年第2期上,张一同志的译文“求sin(α+β)及cos(α+β)”中,用不同于我国现行课本的方法,推导出两角和的正、余弦公式,浅显自然,富有新意,读后受益非浅。笔者用正弦定理及托勒密定理再给出它
In the second issue of this volume in 1986, Comrade Zhang Yi’s translation “Seeking sin(α+β) and cos(α+β)” uses a method different from our current textbook to derive the positive and the cosine of the two-cornered sum. The formula is natural and full of new ideas. After reading it, it benefits a lot. The author uses sine theorem and Ptolemy theorem to give it