Subtangent

The subtangent is a term of analytical geometry. Consider a point on a differentiable curve ( red). If we form the tangent (green). The projection of the tangent to the abscissa means subtangent ( shown in yellow ).

If a curve is differentiable at a point, the subtangent is the distance between the point on the abscissa and the zero point of the tangent.

About the equation of the tangent one attains the zero point and thus the subtangent.

The amount of subtangent the function is constant 1 is true because for all tangents:

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As an analogy to the normal there are subnormal.

• Analytic Geometry