midpoint

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(mĭd'point') pronunciation
n.
  1. Mathematics. The point of a line segment or curvilinear arc that divides it into two parts of the same length.
  2. A position midway between two extremes.

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noun

    A point or an area equidistant from all sides of something: center, median, middle, midst. See edge/center.

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midpoint

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pronunciation

IN BRIEF: In the middle or at the center.

pronunciation We were ready to come home at the midpoint of the trip.

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  1. the point on a line, or a graph, that is equidistant from either end of the line or from two inflections in the graph.
  2. a point in time that is half way between the beginning and the end of an event, or a series of events.

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The midpoint of the segment (x1, y1) to (x2, y2)

In geometry, the midpoint is the middle point of a line segment. It is equidistant from both endpoints.

In statistics and use of histograms, a midpoint is known as class mark.

Contents

Formulas

The formula for determining the midpoint of two points x1 and x2 on a line is:

 \frac{x_1 + x_2}{2}

The formula for determining the midpoint of a segment in the plane, with endpoints (x1, y1) and (x2, y2) in Cartesian coordinates, is:

\left(\frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2}\right)


The formula for determining the midpoint of a segment in the space, with endpoints (x1, y1, z1) and (x2, y2, z2) is:

\left(\frac{x_1 + x_2}{2},\frac{y_1 + y_2}{2}, \frac{z_1 + z_2}{2}\right)

More generally, for an n-dimensional space with axes x_1, x_2, x_3, \dots, x_n\,\!, the midpoint of an interval is given by:

\left(\frac{x_{1_1} + x_{1_2}}{2}, \frac{x_{2_1} + x_{2_2}}{2}, \frac{x_{3_1} + x_{3_2}}{2}, \dots , \frac{x_{n_1} + x_{n_2}}{2} \right)

Construction

Given two points, finding the midpoint is one of the compass and straightedge constructions. The midpoint of a line segment can be located by first constructing a lens using circular arcs, then connecting the cusps of the lens. The point where the cusp-connecting line intersects the segment is then the midpoint. It is more challenging to locate the midpoint using only a compass, but it is still possible.[1]

Generalizations

The midpoint is actually an affine invariant. Hence, aforementioned formulas for Cartesian coordinates are feasible for any affine coordinate system.

The midpoint is not defined in projective geometry. Any point inside a projective range may be projectively mapped to any another point inside (the same or some else) projective range. Fixing one of such points as a midpoint actually defines an affine structure on the projective line containing that range. The projective harmonic conjugate of the two endpoints together with the midpoint is the point at infinity.[2]

The definition of the midpoint of a segment may be extended to geodesic arcs on a Riemannian manifold. Note that, unlike affine case, the midpoint between two points may be defined not uniquely.

See also

References

  1. ^ "Wolfram mathworld". 29 September 2010. http://mathworld.wolfram.com/Midpoint.html. 
  2. ^ H. S. M. Coxeter (1955) The Real Projective Plane, page 119

External links

  • Animation – showing the characteristics of the midpoint of a line segment

Translations:

Midpoint

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Dansk (Danish)
n. - midtpunkt

Nederlands (Dutch)
middelpunt, punt dichtbij het midden

Français (French)
n. - milieu

Deutsch (German)
n. - Mitte

Ελληνική (Greek)
n. - μέσο σημείο, μέσα (γραμμής, γεγονότος κ.λπ.), (στατισ.) μέση τιμή τάξεως

Italiano (Italian)
punto centrale

Português (Portuguese)
n. - ponto central (m)

Русский (Russian)
средняя точка, кульминация

Español (Spanish)
n. - punto medio, mediana

Svenska (Swedish)
n. - mittpunkt

中文(简体)(Chinese (Simplified))
中点, 正中央

中文(繁體)(Chinese (Traditional))
n. - 中點, 正中央

한국어 (Korean)
n. - 중간점

日本語 (Japanese)
n. - 中心点, 中点, 中間点

العربيه (Arabic)
‏(الاسم) نقطه وسط‏

עברית (Hebrew)
n. - ‮נקודת האמצע, אמצע‬


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