(of a line) the state of touching but not crossing a curve at one point

When a line is tangent to a circle, the point of tangency is where the tangent line is perpendicular to the radius of the circle. 当一条直线与圆相切时，切点就是切线垂直于圆半径的地方。

Graphing the equation produces a curve, with tangency occurring at several points along the y-axis.