A rhombus is a special type of quadrilateral that falls under the category of parallelograms, which are foursided figures with opposite sides that are parallel. A rhombus is unique in that all four of its sides are of equal length, and its opposite angles are equal in measure. The sum of the angles in a rhombus is always 360 degrees, making it an interesting shape that has many properties worth exploring. In this comprehensive article, we will delve into the characteristics of a rhombus, its properties, formulas, and why it is represented as ABCD.
Properties of a Rhombus
Sides and Angles
 Equal Sides: A rhombus has four sides of equal length.
 Opposite Angles: The opposite angles in a rhombus are equal in measure.
 Sum of Angles: The sum of the angles in a rhombus is always 360 degrees.
 Diagonals: The diagonals of a rhombus bisect each other at right angles. They are also perpendicular to each other.
Formulas

Area: The area of a rhombus can be calculated using the formula: ( \text{Area} = \frac{d_1 \times d_2}{2} ), where ( d_1 ) and ( d_2 ) are the diagonals of the rhombus.

Perimeter: The perimeter of a rhombus is four times the length of one side (assuming all sides are equal), So, Perimeter = ( 4 \times \text{side} ).
Representing a Rhombus as ABCD
In a geometric representation, a rhombus is shown as a quadrilateral ABCD where:
 A, B, C, and D are the vertices of the rhombus.
 The line segments AB, BC, CD, and DA represent the equal sides of the rhombus.
 The diagonals AC and BD intersect at point O, dividing each other into equal halves.
 The angles marked at the vertices as ∠A, ∠B, ∠C, and ∠D represent the interior angles of the rhombus, with ∠A being opposite to ∠C and ∠B being opposite to ∠D.
Why is a Rhombus Represented as ABCD?
The choice of ABCD in representing a rhombus is arbitrary and is intended to label the vertices in a sequential manner for easy referencing and better visualization in geometric problems. Each letter corresponds to a specific vertex of the rhombus delineating the structure of the shape. By assigning ABCD as the vertices of a rhombus, it becomes easier for mathematicians, students, and teachers to discuss and solve problems related to this geometrical figure.
Common Properties and Characteristics

Symmetry: A rhombus possesses 2 lines of symmetry passing through its opposite vertices.

Diagonal Properties:
a. Bisecting: The diagonals of a rhombus bisect each other at a 90degree angle.
b. Equal Length: The diagonals of a rhombus are of equal length. 
Interior Angles:
a. The interior angles of a rhombus are not right angles but are equal in measure.
b. The diagonals of a rhombus divide the quadrilateral into four congruent triangles. 
Circumscribed Circle: A rhombus can be circumscribed by a circle where all four vertices lie on the circumference of the circle.

Relationship with Squares: A rhombus can be seen as a stretched square, where the angles are not necessarily right angles but maintain equal sides.
Frequently Asked Questions (FAQs)
1. What is the difference between a rhombus and a square?
A rhombus is a quadrilateral with all sides of equal length but with opposite angles not being right angles. A square, on the other hand, is a special case of a rhombus where all sides are equal in length, and all angles are right angles.
2. Can a rhombus have right angles?
Yes, a rhombus can have right angles. However, not all rhombuses have right angles. A rhombus is defined by having all sides equal, but the angles can vary in measure.
3. How can I find the area of a rhombus if only the side length is given?
If you are given the side length of a rhombus, you can find the area by using the formula: Area = side * height, where the height can be calculated using the Pythagorean theorem and half of one of the diagonals.
4. Are the diagonals of a rhombus always perpendicular?
Yes, the diagonals of a rhombus are always perpendicular to each other. This property distinguishes a rhombus from other quadrilaterals.
5. Can a rhombus have equal diagonals?
Yes, in a rhombus, the diagonals are always of equal length, as they bisect each other and form right angles at the point of intersection.
6. What is the difference between a rhombus and a rectangle?
A rhombus is a quadrilateral with all sides equal, whereas a rectangle is a quadrilateral with opposite sides equal and all angles at right angles.
7. How many lines of symmetry does a rhombus have?
A rhombus has two lines of symmetry, passing through the opposite vertices or through the midpoints of opposite sides.
8. Can a rhombus have equal adjacent angles?
No, by definition, a rhombus cannot have equal adjacent angles. The angles opposite to each other are equal, but adjacent angles are distinct in measure.
9. How can I prove that a quadrilateral is a rhombus?
To prove that a quadrilateral is a rhombus, you must demonstrate that it has all sides of equal length and that its diagonals bisect each other at right angles.
10. Is a rhombus always a parallelogram?
Yes, a rhombus is always a parallelogram. It has parallel opposite sides like any other parallelogram but with the additional property of all sides being equal in length.
In conclusion, a rhombus is a fascinating geometric shape with unique properties that distinguish it from other quadrilaterals. Understanding its representation as ABCD and the reasons behind it helps in visualizing and solving problems related to this figure. Its symmetrical nature, equal side lengths, perpendicular diagonals, and relationship with squares make it an important element in geometry with various applications and implications in mathematics and beyond.