tangent of lead angle

例句：

1. 1. The anglebetween the two tangents is90 degrees.
   两个切线的夹角是90度。
2. 2. The circle has aradius of 5 units and a tangent at its center.
   这个圆的半径是5单位，且在圆心处有一条切线。
3. 3. The line that divides the two tangents is calledthe bisector.
   将两条切线分开的直线被称为中线。