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  2. Varignon's theorem - Wikipedia

    en.wikipedia.org/wiki/Varignon's_theorem

    An arbitrary quadrilateral and its diagonals. Bases of similar triangles are parallel to the blue diagonal. Ditto for the red diagonal. The base pairs form a parallelogram with half the area of the quadrilateral, A q, as the sum of the areas of the four large triangles, A l is 2 A q (each of the two pairs reconstructs the quadrilateral) while that of the small triangles, A s is a quarter of A ...

  3. Euler's quadrilateral theorem - Wikipedia

    en.wikipedia.org/wiki/Euler's_quadrilateral_theorem

    If the quadrilateral is a parallelogram, then the midpoints of the diagonals coincide so that the connecting line segment has length 0. In addition the parallel sides are of equal length, hence Euler's theorem reduces to + = + which is the parallelogram law.

  4. Saccheri quadrilateral - Wikipedia

    en.wikipedia.org/wiki/Saccheri_Quadrilateral

    Saccheri quadrilaterals. A Saccheri quadrilateral is a quadrilateral with two equal sides perpendicular to the base.It is named after Giovanni Gerolamo Saccheri, who used it extensively in his 1733 book Euclides ab omni naevo vindicatus (Euclid freed of every flaw), an attempt to prove the parallel postulate using the method reductio ad absurdum.

  5. Quadrilateral - Wikipedia

    en.wikipedia.org/wiki/Quadrilateral

    There can also be defined a quasinine-point center E as the intersection of the lines E a E c and E b E d, where E a, E b, E c, E d are the nine-point centers of triangles BCD, ACD, ABD, ABC respectively. Then E is the midpoint of OH. [47]

  6. Newton's theorem (quadrilateral) - Wikipedia

    en.wikipedia.org/wiki/Newton's_theorem...

    Given such a configuration the point P is located on the Newton line, that is line EF connecting the midpoints of the diagonals. [1] A tangential quadrilateral with two pairs of parallel sides is a rhombus. In this case, both midpoints and the center of the incircle coincide, and by definition, no Newton line exists.

  7. Newton–Gauss line - Wikipedia

    en.wikipedia.org/wiki/Newton–Gauss_line

    In geometry, the Newton–Gauss line (or Gauss–Newton line) is the line joining the midpoints of the three diagonals of a complete quadrilateral.. The midpoints of the two diagonals of a convex quadrilateral with at most two parallel sides are distinct and thus determine a line, the Newton line.

  8. Anne's theorem - Wikipedia

    en.wikipedia.org/wiki/Anne's_theorem

    If the two sums of areas of opposite triangles are equal: | | + | | = | | + | |, then the point L is located on the Newton line, that is the line which connects E and F. [1] [2] For a parallelogram, the Newton line does not exist since both midpoints of the diagonals coincide with point of intersection of the diagonals.

  9. Newton line - Wikipedia

    en.wikipedia.org/wiki/Newton_line

    E, K, F lie on a common line, the Newton line Not to be confused with Newton-Gauss line or Isaac Newton line . In Euclidean geometry the Newton line is the line that connects the midpoints of the two diagonals in a convex quadrilateral with at most two parallel sides.