Equilateral triangle calculator

Please enter one property of the equilateral triangle

Use symbols: a, h, T, p, r, R


You have entered side a, b and c (as equilateral triangle).

Equilateral triangle.

Sides: a = 11.7   b = 11.7   c = 11.7

Area: T = 59.2755108762
Perimeter: p = 35.1
Semiperimeter: s = 17.55

Angle ∠ A = α = 60° = 1.04771975512 rad
Angle ∠ B = β = 60° = 1.04771975512 rad
Angle ∠ C = γ = 60° = 1.04771975512 rad

Height: ha = 10.13224972243
Height: hb = 10.13224972243
Height: hc = 10.13224972243

Median: ma = 10.13224972243
Median: mb = 10.13224972243
Median: mc = 10.13224972243

Inradius: r = 3.37774990748
Circumradius: R = 6.75549981495

Vertex coordinates: A[11.7; 0] B[0; 0] C[5.85; 10.13224972243]
Centroid: CG[5.85; 3.37774990748]
Coordinates of the circumscribed circle: U[5.85; 3.37774990748]
Coordinates of the inscribed circle: I[5.85; 3.37774990748]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 120° = 1.04771975512 rad
∠ B' = β' = 120° = 1.04771975512 rad
∠ C' = γ' = 120° = 1.04771975512 rad

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How did we calculate this triangle?

1. Input data entered: side a b c (as equilateral triangle)

a = 11.7 ; ; b = 11.7 ; ; c = 11.7 ; ;

2. From we calculate b,c:

b = c = a = 11.7 ; ;


Now we know the lengths of all three sides of the triangle and the triangle is uniquely determined. Next we calculate another its characteristics - same procedure as calculation of the triangle from the known three sides SSS.

a = 11.7 ; ; b = 11.7 ; ; c = 11.7 ; ; : Nr. 1

3. The triangle circumference is the sum of the lengths of its three sides

p = a+b+c = 11.7+11.7+11.7 = 35.1 ; ;

4. Semiperimeter of the triangle

s = fraction{ o }{ 2 } = fraction{ 35.1 }{ 2 } = 17.55 ; ;

5. The triangle area using Heron's formula

T = sqrt{ s(s-a)(s-b)(s-c) } ; ; T = sqrt{ 17.55 * (17.55-11.7)(17.55-11.7)(17.55-11.7) } ; ; T = sqrt{ 3513.54 } = 59.28 ; ;

6. Calculate the heights of the triangle from its area.

T = fraction{ a h _a }{ 2 } ; ; h _a = fraction{ 2 T }{ a } = fraction{ 2 * 59.28 }{ 11.7 } = 10.13 ; ; h _b = fraction{ 2 T }{ b } = fraction{ 2 * 59.28 }{ 11.7 } = 10.13 ; ; h _c = fraction{ 2 T }{ c } = fraction{ 2 * 59.28 }{ 11.7 } = 10.13 ; ;

7. Calculation of the inner angles of the triangle using a Law of Cosines

a**2 = b**2+c**2 - 2bc cos( alpha ) ; ; alpha = arccos( fraction{ a**2-b**2-c**2 }{ 2bc } ) = arccos( fraction{ 11.7**2-11.7**2-11.7**2 }{ 2 * 11.7 * 11.7 } ) = 60° ; ; beta = arccos( fraction{ b**2-a**2-c**2 }{ 2ac } ) = arccos( fraction{ 11.7**2-11.7**2-11.7**2 }{ 2 * 11.7 * 11.7 } ) = 60° ; ; gamma = arccos( fraction{ c**2-a**2-b**2 }{ 2ba } ) = arccos( fraction{ 11.7**2-11.7**2-11.7**2 }{ 2 * 11.7 * 11.7 } ) = 60° ; ;

8. Inradius

T = rs ; ; r = fraction{ T }{ s } = fraction{ 59.28 }{ 17.55 } = 3.38 ; ;

9. Circumradius

R = fraction{ a }{ 2 * sin( alpha ) } = fraction{ 11.7 }{ 2 * sin 60° } = 6.75 ; ;




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