So, just to get you used to this idea, I'm going to draw a level surface of a function of three variables OK, so it's a surface given by the equation w of x, y, z equals some constant c.

为了令你们习惯于这个想法，我画一个三变量函数的等值面,这是一个平面,由函数w=c给出的。

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Lin c, Yang Z, Huang X. The Comprehensive Dictionary of Psychology. Shanghai: Shanghai Educational Publishing House, 2004.

林崇德，杨治良，黄希庭。心理学大辞典。上海：上海教育出版社，2004。

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Wu J. g, C. H. Shi, H. Z. Zhang and W. X. Fei, The Determination of Three Types of Essential Amino Acids Content in Milled Rice by Near Infrared Reflectance Spectroscopy.

吴建国、石春海、张小明和费万辛，用近红外反射光谱法分析稻米三种必需氨基酸含量的研究。

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Wu J. g, C. H. Shi, H. Z. Zhang and W. X. Fei, The Determination of Three Types of Essential Amino Acids Content in Milled Rice by Near Infrared Reflectance Spectroscopy.

吴建国、石春海、张小明和费万辛，用近红外反射光谱法分析稻米三种必需氨基酸含量的研究。

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