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# rectangle

Rectangle. A quadrilateral whose four angles are equal, that is, whose 4 angles are equal to $90^{\circ}$.

*Any rectangle is a parallelogram.*

This follows from angles $\angle BAD$ and $\angle ADC$ adding up $180^{\circ}$.

Since parallelograms have their opposite sides equal, so do rectangles. In the picture, $AB=CD$ and $BC=DA$.

Rectangles are the only parallelograms to be also cyclic (since opposite angles add up $180^{\circ}$.

Notice that every square is also a rectangle, but there are rectangles that are not squares

Rectangles have their two diagonals equal (since triangles $ABC$ and $ABD$ are congruent), A nice result following from this is that the quadrilateral obtained by joining the midpoints of the sides is a rhombus.

Related:

Quadrilateral, Parallelogram, Rhombus, ParallelogramLaw, Square

Type of Math Object:

Definition

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## Mathematics Subject Classification

51-00*no label found*

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