中文辅助说明
调整 h，让曲线上的第二点从左侧或右侧靠近固定点，割线便会逐渐靠近切线。图像同时显示点的位置、割线斜率和差商化简过程，帮助你直观理解导数为什么是割线斜率在 h 趋近于零时的极限。
Gradient from first principles
What happens as approaches zero?
Keep fixed. Changing moves the second point along the curve .
Secant and tangent graph
Secant
Tangent at
The calculation behind the picture
The difference between the two gradients is exactly . Therefore, as approaches zero from either side, the secant approaches the tangent.