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# Triangle Calculation

## Free Online Triangle Calculator

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Enter 3 values, with at least 1 side:
Side a: cm
Side b: cm
Side c: cm
Angle α: °
Angle β: °
Angle γ: °

Perimeter: cm
Area: cm²
Height: cm
a
b
c
α
β
γ

### How did we arrive at this result?

Here is a step-by-step explanation of how we calculated the various values for your triangle:

• Sides of the triangle: We calculated the length of the missing sides using the sine rule or cosine rule, depending on the data you entered. For instance, if side a and side b and angle γ are known, we calculated side c as √(a² + b² - 2abcosγ). In this case, side c is calculated as √((² + ² - 2***cos().
• Angles of the triangle: Using the angle values you entered and the sides we calculated, we determined the missing angles. We did this using the sine rule where sinα/a = sinβ/b = sinγ/c. If, for example, angle α is missing, we calculated angle α as arcsin(a*sinγ/c).
• Perimeter of the triangle: The perimeter of the triangle is the sum of the lengths of all its sides. In this case, the perimeter is calculated as a + b + c.
• Area of the triangle: The area of the triangle is calculated using the formula 1/2ab*sinγ. In this case, the area is calculated as 0.5***sin().
• Height of the triangle: The height of the triangle is calculated using the formula 2*area/base. In this case, taking side c as the base, the height is calculated as 2*/.

## How to Calculate a Triangle?

Triangles are one of the most fundamental shapes in geometry, yet they also possess a surprising degree of complexity. There are many different aspects to consider when working with this shape, including the different types of triangles, how their sides and angles are calculated, and how they can be used in practical applications.

### Types of Triangles and Their Characteristics

#### Equilateral Triangle

An equilateral triangle is a triangle in which all three sides are of equal length. This implies that all three internal angles are also equal, each being 60 degrees.

#### Isosceles Triangle

An isosceles triangle is a triangle with two sides of equal length. The angles opposite these sides are also equal to each other.

#### Scalene Triangle

A scalene triangle, also known as an unequal-sided triangle, is a triangle in which all three sides are of different lengths.

#### Acute Triangle

An acute triangle is a triangle in which all three internal angles are less than 90 degrees.

#### Right Triangle

A right triangle is a triangle in which one of the internal angles is exactly 90 degrees. The side opposite this angle is called the hypotenuse.

#### Obtuse Triangle

An obtuse triangle is a triangle in which one of the internal angles is greater than 90 degrees.

Each triangle is unique in its kind, and recognizing and classifying these different types is an essential aspect of the study of geometry.

### Calculation of the Sides of a Triangle

There are various methods to calculate the sides of a triangle, depending on the information provided. Two of the most common methods are the sine rule and the cosine rule.

The Sine Rule is as follows:

a/sin(A) = b/sin(B) = c/sin(C)

where a, b, c are the side lengths and A, B, C are the opposite angles.

The Cosine Rule is as follows:

c² = a² + b² - 2abcos(C)

where C is the angle between sides a and b.

### Calculation of the Angles of a Triangle

The angles of a triangle can also be calculated using the sine rule or the cosine rule, depending on the given information. Additionally, it's important to remember that the sum of the angles in a triangle always equals 180 degrees.

Let's take an example to illustrate this. Suppose we have a triangle with sides a = 8 cm, b = 6 cm, and c = 7 cm, and we want to calculate the angles of the triangle.

#### The Cosine Rule

The cosine rule is useful when we know the length of all three sides of the triangle. The cosine rule is as follows:

cos(C) = (a² + b² - c²) / 2ab

With the given sides of our example triangle, we can calculate angle C as follows:

cos(C) = (8² + 6² - 7²) / 2*8*6

C = cos⁻¹[(64 + 36 - 49) / 96] = 46.6° (rounded to one decimal)

#### The Sine Rule

The sine rule is useful when we know the length of two sides and a non-included angle. The sine rule is as follows:

a/sin(A) = b/sin(B) = c/sin(C)

With the given sides of our example triangle and the calculated angle C, we can calculate angle A as follows:

A = sin⁻¹[a * sin(C) / c]

A = sin⁻¹[8 * sin(46.6°) / 7] = 63.4° (rounded to one decimal)

Finally, knowing that the sum of the angles in a triangle always equals 180 degrees, we can calculate angle B:

B = 180° - A - C = 180° - 63.4° - 46.6° = 70°

### Pythagoras' Theorem

Pythagoras' theorem is a fundamental relation in geometry that states that in a right-angled triangle the square of the length of the hypotenuse is equal to the sum of the squares of the lengths of the other two sides.

The Pythagoras' Theorem is as follows:

a² + b² = c²

For example, if side a has a length of 3 and side b has a length of 4, then the length of side c (the hypotenuse) is equal to √(3² + 4²) = 5.

### Calculation of the Perimeter of a Triangle

The perimeter of a triangle is simply the sum of the lengths of its sides. So if the sides are a, b, and c, then the perimeter is equal to a + b + c.

### Calculation of the Area of a Triangle

The area of a triangle is typically calculated using the formula:

Area = 1/2 * base * height

For example, if the base of a triangle is 6 units and the height is 4 units, then the area of the triangle is 1/2 * 6 * 4 = 12 square units.

### Calculation of the Height of a Triangle

The height of a triangle can be calculated as the area of the triangle divided by half the length of the base. So height = (2 * Area) / base. For example, if the area of a triangle is 12 square units and the base is 6 units, then the height is 12 / 3 = 4 units.

In conclusion, calculating the properties of a triangle might seem a bit intimidating at first, but with the right formulas and some practice, it can be quite simple and even fun. Whether it's calculating the sides, angles, perimeter, area, or height, these geometric calculations are fundamental to many areas of mathematics and beyond.