A quadrilateral is a four-sided polygon with four angles. There are many kinds ofquadrilaterals. The five most common types are the parallelogram, the rectangle, the square, the trapezoid, and the rhombus. A quadrilateral is a polygon with four edges (or sides) and four vertices or corners. Sometimes, the term quadrangle is used, by analogy with triangle, and sometimes tetragon for consistency with pentagon (5-sided), hexagon (6-sided) and so on. The origin of the word "quadrilateral" is the two Latin words quadri, a variant of four, and latus, meaning "side". Quadrilaterals are simple (not self-intersecting) or complex (self-intersecting), also called crossed. Simple quadrilaterals are either convex or concave. The interior angles of a simple (and planar) quadrilateral ABCD add up to 360 degrees of arc, that is {displaystyle angle A+angle B+angle C+angle D=360^{circ }.} angle A+angle B+angle C+angle D=360^{circ }. This is a special case of the n-gon interior angle sum formula (n − 2) × 180°. All non-self-crossing quadrilaterals tile the plane by repeated rotation around the midpoints of their edges.

A quadrilateral is a four-sided polygon with four angles. There are many kinds ofquadrilaterals. The five most common types are the parallelogram, the rectangle, the square, the trapezoid, and the rhombus. A quadrilateral is a polygon with four edges (or sides) and four vertices or corners. Sometimes, the term quadrangle is used, by analogy with triangle, and sometimes tetragon for consistency with pentagon (5-sided), hexagon (6-sided) and so on. The origin of the word "quadrilateral" is the two Latin words quadri, a variant of four, and latus, meaning "side". Quadrilaterals are simple (not self-intersecting) or complex (self-intersecting), also called crossed. Simple quadrilaterals are either convex or concave. The interior angles of a simple (and planar) quadrilateral ABCD add up to 360 degrees of arc, that is {displaystyle angle A+angle B+angle C+angle D=360^{circ }.} angle A+angle B+angle C+angle D=360^{circ }. This is a special case of the n-gon interior angle sum formula (n − 2) × 180°. All non-self-crossing quadrilaterals tile the plane by repeated rotation around the midpoints of their edges.

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