wǒ men / xū yào / jì suàn / zhè tiáo / qū xiàn / zài / gěi dìng / diǎn / de / dān wèi qiē xiàng liàng我们需要计算这条曲线在给定点的单位切向量。We need to calculate the unit tangent vector of this curve at a given point.