21. Sometimes the slopes of the left and right tangent lines are equal, so the tangent lines coincide. 22. Sometimes the slopes of the left and right tangent lines are equal, so the tangent lines coincide. 23. The tangent lines to a cubic at three collinear points intercept the cubic again at collinear points. 24. Any point in the plane is on either zero, one or two tangent lines of a conic. 25. The concept of a tangent line to one or more circles can be generalized in several ways. 26. See also Tangent lines to circles. 27. The tangent lines containing the sides of the tangential triangle are called the "'exsymmedians "'of the reference triangle. 28. At each point of an ovoid all the tangent lines to the ovoid lie in a single plane. 29. The radius of a circle is perpendicular to the tangent line through its endpoint on the circle's circumference. 30. If intersects in only one point, then it is a tangent line and is the point of tangency.
