Unit Circle
Core Sentence / 核心句
The unit circle gives geometric meaning to sine, cosine, and their derivatives.
中文理解：单位圆把三角函数从记忆表变成几何运动。
Formula / 公式或规则
On the unit circle:
When To Use / 什么时候用
看到 sine/cosine geometry、radians、circular motion，就回到 unit circle。
Watch Out / 易错点
不要把 sin/cos 只当成计算器按钮；它们是圆上坐标。
Search and Source Mentions / 搜索与出现位置
Mentioned In / 出现位置
- 03 - Derivative Formulas through Geometry · Knowledge Point 7: Why $\frac{d}{d\theta}\sin\theta=\cos\theta$
在 Unit Circle 里：
- 03 - Derivative Formulas through Geometry · 5. The derivative of sine is cosine.
The derivative of sine is cosine because the tiny change in height divided by the tiny arc-length step equals adjacent over hypotenuse on the unit circle.
- 03 - Derivative Formulas through Geometry · 2. Class Flow / 视频脉络
6. 用 Unit Circle 解释为什么：