直角三角形有一个角是直角。

A right triangle has a right Angle.

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直角三角形的斜边是直角三角形中最长的边。

The hypotenuse is the longest side of a right triangle.

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一些人需要复习一点数学课程，正弦的作用是给出在一个直角三角形中的一个已知角所对应的一条边与直角三角形斜边之间的比率。

For anyone that needs a little refresher course, the sine function gives the ratio of the opposite side of a given Angle in a right triangle to the hypotenuse.

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May hurt a little bit, but try as much as possible to create a 90 degree angle.

可能有点痛，尽可能形成一个直角。

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Now take these two fingers-- the middle finger and the thumb-- and as much as possible, from that 90 degree angle, create a circle.

再让这两个手指-,中指和姆指-,尽可能保持直角时围成一个圆圈。

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And, moreover, they are at right angles to one another that we've learned.

更多的是，根据我们所学的知识,它们都是和另外一个互成直角。

麻省理工公开课 - 固态化学导论课程节选