Cosine
Core Sentence / 核心句
Cosine is the x-coordinate of a point on the unit circle.
中文理解：余弦可以理解成单位圆上的横坐标。
Formula / 公式或规则
When To Use / 什么时候用
看到 unit circle、cos derivative、trig geometry，就用 cosine。
Watch Out / 易错点
三角函数导数默认 radians。
Search and Source Mentions / 搜索与出现位置
Mentioned In / 出现位置
- 03 - Derivative Formulas through Geometry · 5. The derivative of sine is cosine.
5. The derivative of sine is cosine.
- 03 - Derivative Formulas through Geometry · Knowledge Point 7: Why $\frac{d}{d\theta}\sin\theta=\cos\theta$
Adjacent divided by hypotenuse is exactly what cosine means.