tangent roundabout

例句：

1. 1. The tangentof a circle is the length of itscircumference.
   圆的切线是其周长的长度。
2. 2. The tangent to this curve is at an angleof 30 degrees.
   这个曲线的切线与x轴成30度角。
3. 3. The tangent line dividesthe circle into two equal parts.
   切线将圆分成两个相等的部分。