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Rhombus

A rhombus  is a quadrilateral whose four sides all have the same length.
A rhombus has four equal sides, opposite sides that are parallel, equal opposite angles and diagonals that bisect at right angles.

Diagonals are DB = d1   and  AC = d2   

DB ⊥ AC

Properties of Rhombus Reference
   

All sides of a rhombus are congruent (equal).

AB = CD = DA = BC

Diagonals bisect each other at 90° or we can also say that each of the two diagonals in a rhombus is the perpendicular bisector of the other.

Diagonals DB and CA bisect each other at 90°

The opposite sides are parallel.

Opposite angles are equal

CD || AB and BC || AD.

∠A = ∠C and ∠D = ∠B
Adjacent angles add up to 180°

∠A + ∠B = 180°

∠B + ∠C = 180°

∠C + ∠D = 180°

∠A + ∠D = 180°

 

Area 
Perimeter

Area = ah

Perimeter = 4⋅a