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The secant lines PQ are the approximations to the tangent line. In calculus, this idea is the geometric definition of the derivative. The tangent line at point P is a secant line of the curve. A tangent line to a curve at a point P may be a secant line to that curve if it intersects the curve in at least one point other than P.
This leads to the definition of the slope of the tangent line to the graph as the limit of the difference quotients for the function f. This limit is the derivative of the function f at x = a, denoted f ′(a). Using derivatives, the equation of the tangent line can be stated as follows: = + ′ ().
Tangent line at (x 0, f(x 0)). The derivative f′(x) of a curve at a point is the slope (rise over run) of the line tangent to that curve at that point. Differential calculus is the study of the definition, properties, and applications of the derivative of a function. The process of finding the derivative is called differentiation. Given a ...
Tangent to a curve. The red line is tangential to the curve at the point marked by a red dot. In Euclidean geometry, all lines are congruent, meaning that every line can be obtained by moving a specific line. However, lines may play special roles with respect to other geometric objects and can be classified according to that relationship.
For example, the sine of angle θ is defined as being the length of the opposite side divided by the length of the hypotenuse. The six trigonometric functions are defined for every real number , except, for some of them, for angles that differ from 0 by a multiple of the right angle (90°).
The names exsecant, versine, chord, etc. can also be applied to line segments related to a circular arc. [2] The length of each segment is the radius times the corresponding trigonometric function of the angle. The external secant function (abbreviated exsecant, symbolized exsec) is a trigonometric function defined in terms of the secant function:
Next to the intersecting chords theorem and the tangent-secant theorem, the intersecting secants theorem represents one of the three basic cases of a more general theorem about two intersecting lines and a circle - the power of point theorem.
Secant-, chord-theorem. For the intersecting secants theorem and chord theorem the power of a point plays the role of an invariant: . Intersecting secants theorem: For a point outside a circle and the intersection points , of a secant line with the following statement is true: | | | | = (), hence the product is independent of line .