An Etymological Dictionary of Astronomy and Astrophysics

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فرهنگ ریشه‌شناختی اخترشناسی-اخترفیزیک

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law of cosines
  قانون ِ کوسینوس‌ها  
qânun-e kosinushâ
Fr.: loi des cosinus  

An expression that for any triangle relates the length of a side to the cosine of the opposite angle and the lengths of the two other sides. If a, b, and c are the sides and A, B, and C are the corresponding opposites angles:

a2 = b2 + c2

  • 2bc cos A; b2 = c2 + a2
  • 2ca cos B; c2 = a2 + b2
  • 2ab cos C.

See also: → law; → cosine.