Rhombus Calculator

Data Source & Methodology

A rhombus is a quadrilateral with all four sides of equal length. It is a special type of parallelogram. Its properties are derived from foundational geometric principles, including the **Pythagorean Theorem** and **Trigonometric Laws** (Sine, Cosine).

• Authoritative Source: The methods are based on **Euclid's *Elements*** (Book I, definitions and propositions related to parallelograms) and standard trigonometric identities.
• Methodology: "Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte." The core strategy involves using the two right triangles formed by either the height, or the four right triangles formed by the intersecting diagonals, to solve the entire figure.

The Formulas Explained

A rhombus can be solved if you know two sufficient properties. The most common formulas are based on diagonals ($p, q$), or side and angle ($a, \alpha$).

1. Using Diagonals ($p, q$)

The diagonals of a rhombus bisect each other at a 90° right angle. This creates four congruent right triangles with legs $p/2$ and $q/2$, and hypotenuse $a$.

Area ($A$):

Side ($a$):

2. Using Side ($a$) and an Angle ($\alpha$)

The area can also be found like any parallelogram: base times height. The height ($h$) is $a \sin(\alpha)$.

Area ($A$):

Height ($h$):

Diagonals ($p, q$) from Side and Angle:

3. Key Relationships

Perimeter ($P$):

Angle Sum:

Glossary of Variables

• Side ($a$): The length of one of the four equal sides.
• Diagonal ($p$): The length of the *longer* diagonal (vertex to vertex).
• Diagonal ($q$): The length of the *shorter* diagonal.
• Height ($h$): The perpendicular distance between two opposite sides.
• Acute Angle ($\alpha$): The smaller of the two internal angles (must be $\le 90^\circ$).
• Obtuse Angle ($\beta$): The larger of the two internal angles (must be $\ge 90^\circ$).
• Area ($A$): The total space enclosed by the rhombus.
• Perimeter ($P$): The total distance around the rhombus's boundary.

How It Works: A Step-by-Step Example

Let's solve a rhombus where you only know the **side ($a$)** and the **height ($h$)**.

Problem: You have a rhombus with a **side of 10 in** and a **height of 8 in**. Find all its properties.

1. Enter Known Values:

   In the calculator, you would enter "10" for Side (a) and "8" for Height (h). Press "Calculate".

2. Step 1: Find Area ($A$) and Perimeter ($P$):

   These are the most direct calculations.

   $$ A = \text{base} \times \text{height} = a \times h = 10 \times 8 = 80 \text{ in}^2 $$ $$ P = 4a = 4 \times 10 = 40 \text{ in} $$
3. Step 2: Find Angles ($\alpha, \beta$):

   The calculator uses the height formula $h = a \sin(\alpha)$ in reverse.

   $$ \sin(\alpha) = h / a = 8 / 10 = 0.8 $$ $$ \alpha = \arcsin(0.8) \approx 53.13^\circ $$ $$ \beta = 180^\circ - \alpha = 180^\circ - 53.13^\circ = 126.87^\circ $$
4. Step 3: Find Diagonals ($p, q$):

   Now, using the side and newly found angles, we can find the diagonals.

   $$ q = 2a \sin(\alpha/2) = 2(10) \sin(53.13^\circ/2) = 20 \sin(26.565^\circ) \approx 8.944 \text{ in} $$ $$ p = 2a \cos(\alpha/2) = 2(10) \cos(26.565^\circ) = 20 \cos(26.565^\circ) \approx 17.888 \text{ in} $$

Result: The calculator would fill in all remaining fields with these computed values.

Frequently Asked Questions (FAQ)