limit curve的用法和樣例：
例句
- Then we discuss the necessary conditions for the limit curve to be C0,C1,C2 respectively and give the derivative and second derivative of the limit curve at vertex and midpoint.
隨后我們討論了極限曲線(xiàn)連續，一階連續，二階連續的必要條件，并給出了極限曲線(xiàn)在頂點(diǎn)以及中點(diǎn)處的一階導數與二階導數顯式公式。
