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  2. Parallelogram - Wikipedia

    en.wikipedia.org/wiki/Parallelogram

    In Euclidean geometry, a parallelogram is a simple (non- self-intersecting) quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equal measure. The congruence of opposite sides and opposite angles is a direct consequence of the ...

  3. Rhombus - Wikipedia

    en.wikipedia.org/wiki/Rhombus

    A rhombus therefore has all of the properties of a parallelogram: for example, opposite sides are parallel; adjacent angles are supplementary; the two diagonals bisect one another; any line through the midpoint bisects the area; and the sum of the squares of the sides equals the sum of the squares of the diagonals (the parallelogram law).

  4. Parallelogon - Wikipedia

    en.wikipedia.org/wiki/Parallelogon

    In geometry, a parallelogon is a polygon with parallel opposite sides (hence the name) that can tile a plane by translation (rotation is not permitted). [1][2] Parallelogons have an even number of sides and opposite sides that are equal in length. A less obvious corollary is that parallelogons can only have either four or six sides; [1 ...

  5. Conway criterion - Wikipedia

    en.wikipedia.org/wiki/Conway_criterion

    In its simplest form, the criterion simply states that any hexagon with a pair of opposite sides that are parallel and congruent will tessellate the plane. [8] In Gardner's article, this is called a type 1 hexagon. [7] This is also true of parallelograms.

  6. Quadrilateral - Wikipedia

    en.wikipedia.org/wiki/Quadrilateral

    Parallelogram: a quadrilateral with two pairs of parallel sides. Equivalent conditions are that opposite sides are of equal length; that opposite angles are equal; or that the diagonals bisect each other. Parallelograms include rhombi (including those rectangles called squares) and rhomboids (including those rectangles called oblongs).

  7. Congruence (geometry) - Wikipedia

    en.wikipedia.org/wiki/Congruence_(geometry)

    Congruence permits alteration of some properties, such as location and orientation, but leaves others unchanged, like distances and angles. The unchanged properties are called invariants. In geometry, two figures or objects are congruent if they have the same shape and size, or if one has the same shape and size as the mirror image of the other.

  8. Lexell's theorem - Wikipedia

    en.wikipedia.org/wiki/Lexell's_theorem

    The two diagonals and bisect each-other and the figure has 2-fold rotational symmetry about the intersection point (so the diagonals each split the parallelogram into two congruent spherical triangles, and ); if the midpoints of either pair of opposite sides are connected by a great circle , the four vertices fall on two parallel small circles ...

  9. Parallelogram law - Wikipedia

    en.wikipedia.org/wiki/Parallelogram_law

    The sum of the areas of the blue squares equal that of the red ones. In mathematics, the simplest form of the parallelogram law (also called the parallelogram identity) belongs to elementary geometry. It states that the sum of the squares of the lengths of the four sides of a parallelogram equals the sum of the squares of the lengths of the two ...