# 20 20 20 triangle

### Equilateral triangle.

Sides: a = 20   b = 20   c = 20

Area: T = 173.2055080757
Perimeter: p = 60
Semiperimeter: s = 30

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

Height: ha = 17.32105080757
Height: hb = 17.32105080757
Height: hc = 17.32105080757

Median: ma = 17.32105080757
Median: mb = 17.32105080757
Median: mc = 17.32105080757

Inradius: r = 5.77435026919
Circumradius: R = 11.54770053838

Vertex coordinates: A[20; 0] B[0; 0] C[10; 17.32105080757]
Centroid: CG[10; 5.77435026919]
Coordinates of the circumscribed circle: U[10; 5.77435026919]
Coordinates of the inscribed circle: I[10; 5.77435026919]

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

# How did we calculate this triangle?

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. ### 1. The triangle circumference is the sum of the lengths of its three sides ### 2. Semiperimeter of the triangle ### 3. The triangle area using Heron's formula ### 4. Calculate the heights of the triangle from its area. ### 5. Calculation of the inner angles of the triangle using a Law of Cosines    