求翻译：教学有一个显著的特点，就是在中唯一能够看到的就是他的手，不断地书写一些数学的符号，并缓慢地填满整个屏幕。除此之外，就是配合书写进行讲解的画外音。是什么意思？

Instructional video has a remarkable characteristic, that is the only way to see in the video is his hand , continue to write some mathematical symbols , and slowly fill the entire screen .

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The teaching video frequency has a remarkable characteristic, is only can see in the video frequency is his hand, writes some mathematics unceasingly the mark, and fills up the entire screen slowly.In addition, is coordinates writing to carry on the explanation the offscreen voice.

Instructional videos have a striking feature, is only able to see in the video was his hand, continue to write some mathematical symbols, and slowly fill the entire screen. In addition, is to coordinate the writing explains voiceover.

正在翻译，请等待...