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Triangle Calculator

Enter the required values and click on the "CALCULATE" button to get instant and accurate solution.

Input 3 values containing at least one side to the following six (6) fields.

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The triangle calculator helps you quickly determine unknown sides, angles, heights, medians, area, and more. It simplifies complex trigonometry calculations for students, teachers, and professionals.

Triangle Facts:

  • A triangle cannot contain more than one obtuse angle.
  • The sum of all interior angles is always 180°.
  • The sum of any two interior angles equals the exterior angle opposite the remaining side.
  • Triangles are classified by their sides and angles: Right, Acute, Obtuse, Isosceles, Scalene, and Equilateral Triangle.

Triangle

Calculating Height and Area of a Triangle

Height of a Triangle:

The height can be calculated as:

\(\ h = \frac{2A}{b} \)

  • A = area of the triangle
  • b = base of the triangle

Area of a Triangle:

The area is determined by:

\(\ \text{Area} = \frac{1}{2} b h \)

  • b = base
  • h = height

If all three sides are known, Heron’s formula can be used:

\(\ s = \frac{a+b+c}{2} \)

\(\ \text{Area} = \sqrt{s(s-a)(s-b)(s-c)} \)

Finding Sides and Angles of a Triangle

Triangles consist of three sides and three angles. You can calculate unknown values using the Pythagorean theorem, Law of Sines, or Law of Cosines.

Law of Sines:

The Law of Sines is useful for finding unknown sides or angles:

\(\frac{a}{\sin A} = \frac{b}{\sin B} = \frac{c}{\sin C}\)

For right triangles with known hypotenuse:

\(a = c \cdot \sin \alpha \quad\text{or}\quad a = c \cdot \cos \beta\)

\(b = c \cdot \sin \beta \quad\text{or}\quad b = c \cdot \cos \alpha\)

Pythagorean Theorem:

In right triangles, if two sides are known, the third can be found:

\(a^2 + b^2 = c^2\)

For unknown sides:

\(a = \sqrt{c^2 - b^2}\)

\(c = \sqrt{a^2 + b^2}\)

Law of Cosines:

The Law of Cosines works for any triangle:

\(a^2 = b^2 + c^2 - 2bc \cdot \cos A\), so \(\cos A = \frac{b^2 + c^2 - a^2}{2bc}\)

\(b^2 = a^2 + c^2 - 2ac \cdot \cos B\), so \(\cos B = \frac{a^2 + c^2 - b^2}{2ac}\)

\(c^2 = a^2 + b^2 - 2ab \cdot \cos C\), so \(\cos C = \frac{a^2 + b^2 - c^2}{2ab}\)

Finding Missing Sides Using Trigonometry:

If one side and one angle are known:

a = b \cdot \tan \alpha

b = a \cdot \tan \beta

If the area and one side are known:

b = \frac{2 \cdot \text{Area}}{a}

c = \sqrt{a^2 + (\frac{2 \cdot \text{Area}}{a})^2}

Calculating Inradius and Circumradius

Inradius:

The inradius is the radius of the circle inscribed in the triangle:

\(r = \frac{\text{Area}}{s}\)

Inradius

Circumradius:

The circumradius is the radius of the circle passing through all triangle vertices:

\(R = \frac{a}{2 \sin A}\)

Circumradius

Example:

Given:

  • \(a = 2\)
  • \(m\angle A = 60^\circ\)
  • \(m\angle B = 20^\circ\)

Step 1: Find the Third Angle

\(m\angle C = 180^\circ - A - B = 100^\circ\)

Convert angles to radians:

\(A = 1.0472 \text{ rad},\ B = 0.34907 \text{ rad},\ C = 1.74533 \text{ rad}\)

Step 2: Find Remaining Sides Using Law of Sines

\(b = \frac{a \cdot \sin B}{\sin A} = 0.78986\)

\(c = \frac{a \cdot \sin C}{\sin A} = 2.27432\)

Step 3: Calculate Area

\(A = \frac{ab \cdot \sin C}{2} = 0.77786\)

Step 4: Perimeter and Semiperimeter

\(p = a + b + c = 5.06418\)

\(s = \frac{p}{2} = 2.53209\)

Step 5: Heights

\(h_a = \frac{2A}{a} = 0.77786\)

\(h_b = \frac{2A}{b} = 1.96961\)

\(h_c = \frac{2A}{c} = 0.68404\)

Step 6: Medians

\(m_a = 1.37775, \ m_b = 2.10482, \ m_c = 1.00936\)

Step 7: Inradius

\(r = \frac{A}{s} = 0.3072\)

Step 8: Circumradius

\(R = \frac{a}{2 \sin A} = 1.1547\)

Other Languages: Výpočet Trojúhelníku, Calculer Triangle, Dreieck Rechner, Kalkulator Segitiga, Kalkulator Trójkata, Калькулятор Треугольника, Calcular Triangulo, Üçgen Hesaplama, Calculadora De Triángulos

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