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The Pythagorean trigonometric identity is a trigonometric identity expressing the Pythagorean theorem in terms of trigonometric functions. Along with the sum-of-angles formulae, it is one of the basic relations between the sine and cosine functions. The identity is given by the formula: : (Note that means . This relation between sine and cosine is sometimes called the fundamental Pythagorean trigonometric identity.〔 〕 If the length of the hypotenuse of a right triangle is 1, then the length of either of the legs is the sine of the opposite angle and is also the cosine of the adjacent acute angle. Therefore, this trigonometric identity follows from the Pythagorean theorem. ==Proofs and their relationships to the Pythagorean theorem== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pythagorean trigonometric identity」の詳細全文を読む スポンサード リンク
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