【李永乐老师】周期函数如何展开成一系列的三角函数？《火柴人vs数学》深度解析（二）泰勒展开

Picked video by video from 李永乐老师 (mixed channel): title plainly names a teaching subject. Channel transcript sample: All three samples lack transcripts, so no direct evidence of teaching substance could be verified, but prior title-sample verdict and channel pattern support a 'pick' classification for video-by-video review.

A 11-minute video from 李永乐老师: “【李永乐老师】周期函数如何展开成一系列的三角函数？《火柴人vs数学》深度解析（二）泰勒展开”.

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