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Also, side AB is equal in length to side DC, since opposite sides of a parallelogram are equal in length. Therefore, triangles ABE and CDE are congruent (ASA postulate, two corresponding angles and the included side). Therefore, = =. Since the diagonals AC and BD divide each other into segments of equal length, the diagonals bisect each other.
Isosceles trapezoid. In Euclidean geometry, an isosceles trapezoid (isosceles trapezium in British English) is a convex quadrilateral with a line of symmetry bisecting one pair of opposite sides. It is a special case of a trapezoid. Alternatively, it can be defined as a trapezoid in which both legs and both base angles are of equal measure, [ 1 ...
The rhombus has a square as a special case, and is a special case of a kiteand parallelogram. In plane Euclidean geometry, a rhombus(pl.: rhombior rhombuses) is a quadrilateralwhose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length.
Geometrical theorem relating the lengths of two segments that divide a triangle. The theorem states for any triangle ∠ DAB and ∠ DAC where AD is a bisector, then. In geometry, the angle bisector theorem is concerned with the relative lengths of the two segments that a triangle 's side is divided into by a line that bisects the opposite angle.
The angle between a side and a diagonal is equal to the angle between the opposite side and the same diagonal. The diagonals cut each other in mutually the same ratio (this ratio is the same as that between the lengths of the parallel sides). The diagonals cut the quadrilateral into four triangles of which one opposite pair have equal areas ...
Equidiagonal quadrilateral: the diagonals are of equal length. Bisect-diagonal quadrilateral: one diagonal bisects the other into equal lengths. Every dart and kite is bisect-diagonal. When both diagonals bisect another, it's a parallelogram. Ex-tangential quadrilateral: the four extensions of the sides are tangent to an excircle.
The central angle of a square is equal to 90° (360°/4). The external angle of a square is equal to 90°. The diagonals of a square are equal and bisect each other, meeting at 90°. The diagonal of a square bisects its internal angle, forming adjacent angles of 45°. All four sides of a square are equal. Opposite sides of a square are parallel.
Thales's theorem can also be used to find the centre of a circle using an object with a right angle, such as a set square or rectangular sheet of paper larger than the circle. [7] The angle is placed anywhere on its circumference (figure 1). The intersections of the two sides with the circumference define a diameter (figure 2).