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