它们也能表现为描述一个可定义概念或理论概念的性质，如“一切三角形都有三条边”。

They may also take the form of describing properties of a definable or theoretic concept, such as 'all triangles have three sides'.

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本文讨论了三角函数在有理度数上的取值的代数性质，得出其取值均为代数数。

This paper discusses an algebraic property of values of rational degrees of triangle functions. We obtain that they are all algebraic Numbers.

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摘要利用由三角级数和幂级数复合构成的函数项级数的有关性质，得到了一类变系数非齐次调和方程边值问题的级数解。

In this paper by using the property of Fourier series a compound series consisting of trigonometric series and power series is established.

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You can square this guy and add it to the square of this guy and you will find, using the magic of trigonometry, that this is true.

你可以把这两个式子平方相加,再用一下三角函数的性质,你会发现这是正确的

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